VIA EDGAR AND OVERNIGHT DELIVERY

U.S. Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Ladies and Gentlemen:

On behalf of Sutro Biopharma, Inc. (the “Company”), we are concurrently transmitting herewith Confidential Submission No. 2 (“Draft No. 2”) to the Confidential Draft Registration Statement on Form S-1 (CIK No. 0001382101) confidentially submitted by the Company to the U.S. Securities and Exchange Commission (the “Commission”) on June 1, 2018 (the “Draft Registration Statement”). In this letter, we respond to the comments of the staff of the Commission (the “Staff”) contained in the Staff’s letter dated June 29, 2018 (the “Letter”). The numbered paragraphs below correspond to the numbered comments in the Letter and the Staff’s comments are presented in bold italics. We have also enclosed with the copy of this letter that is being transmitted via overnight courier copies of Draft No. 2 in paper format, marked to show changes from the Draft Registration Statement as initially submitted.

In addition to addressing the comments raised by the Staff in the Letter, the Company has revised Draft No. 2 to update certain other disclosures.

Prospectus Summary, page 1

U.S. Securities and Exchange Commission

July 10, 2018

Page 2

In response to the Staff’s comment, the Company has revised its disclosure on pages 2, 3, 95, 107 and 111 of Draft No. 2 to clarify that additional studies will be needed to determine the safety and efficacy of the Company’s product candidates, that the results of these studies may be different than the results of earlier studies, and that the Company’s product candidates have not and will not receive regulatory approval unless the FDA or foreign regulatory agencies determine they are safe and effective. To ensure that the disclosure is fair and balanced, the Company has placed this new disclosure immediately following the first discussion of the studies.

The Company advises the Staff that it believes that its product candidates have the potential to be best-in-class based on preclinical data generated to date. Specifically, STRO-001’s and STRO-002’s homogenous designs suggest that they can provide greater anti-tumor activity, stability and safety than competing therapies. The Company also believes that STRO-001 has the potential to be first-in-class given it is currently the most advanced product candidate in the clinic targeting the antigen CD74, which is highly expressed in many B cell malignancies, including multiple myeloma and lymphoma. Additionally, the Company believes its XpressCF Platform allows it to accelerate the discovery and development of potential best-in-class and/or first-in-class molecules due to its unique characteristics and versatility.

In response to the Staff’s comment, the Company has revised its disclosure on pages 1, 2, 4, 79, 94, 95, 96, 104 and 106 of Draft No. 2, in some cases to delete references to first-in-class and best-in-class and in other cases to make clear that the Company’s product candidates and the molecules discovered from the Company’s XpressCF Platform are not currently, but have the potential in the future to be, best-in-class and/or first-in-class. The Company has also added disclosure on pages 2, 3 and 95 clarifying that additional studies will be needed to determine the safety and efficacy of the Company’s product candidates, the Company’s product candidates have not yet received regulatory approval and may not receive regulatory approval, if at all, prior to competing products, and competing therapies may ultimately reach market faster and have more favorable safety and efficacy profiles.

Our Pipeline, page 2

In response to the Staff’s comment, the Company has revised its disclosure on pages 2 and 105 of Draft No. 2 to include columns for Phases 2 and 3. The Company has also included the indications inside the arrows on the pipeline chart.

Additionally, the Company advises the Staff that it believes its discovery phase programs are material to an understanding of the Company’s overall development program and strategy. It believes the existence of the Company’s IL-2 mimetic, oncology and I/O programs, as well as it’s collaboration with Merck KGaA, Darmstadt, Germany to develop additional antibody-drug conjugates, helps provide investors with a complete picture of the Company’s current development plans and future strategies, and helps convey the breadth of the Company’s pipeline and development capabilities. The Company therefore believes the inclusion of the discovery phase programs in its pipeline chart provides important information and context for investors.

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U.S. Securities and Exchange Commission

July 10, 2018

Page 3

Corporate Information, page 5

In response to the Staff’s comment, the Company has revised its disclosure on page 122 of Draft No. 2.

Use of Proceeds, page 68

In response to the Staff’s comment, the Company has revised its disclosure on page 68 of Draft No. 2 to leave spaces showing the location where the Company will add disclosure, prior to launching the road show for this offering, for the expected stage of development that the Company expects to achieve with its current assets and proceeds from this offering.

Management’s Discussion and Analysis of Financial Condition and Results of Operations, page 79

Critical Accounting Polices and Estimates, page 88

Stock-Based Compensation, page 90

In response to the first part of the Staff’s comment, the Company has revised its disclosure on page 91 of Draft No. 2. Additionally, the Company will update such disclosure to specify the methods used to determine the fair value of the shares underlying awards granted through June 30, 2018 when the updated financial statements as of and for the six months ended June 30, 2018 are included in the Registration Statement.

With respect to the second part of the Staff’s comment, the Company acknowledges the Staff’s comment and will supplementally provide the requested information once the estimated offering price range has been determined.

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U.S. Securities and Exchange Commission

July 10, 2018

Page 4

Business, page 94

Our Product Candidates, page 104

In response to the Staff’s comment, the Company has revised its disclosure on pages 107 and 112 of Draft No. 2 to include additional detail regarding these studies and to clarify that the mouse models do not address safety. The Company advises the Staff that mouse tumor models are used in the industry to provide proof-of-concept preclinical data to demonstrate that an experimental anti-cancer agent has the potential to treat human disease. Various tumor cell lines are implanted in living mice and allowed to grow, but ultimately the mice will succumb to the tumor. Experimental agents such as STRO-001 and STRO-002 are administered to the mice and assessed for tumor shrinkage and/or survival of the mouse, as depicted in the data presented in the Registration Statement. Mouse tumor models do not test for safety and they are not considered toxicology models by the FDA. In order to test for safety, the FDA requires testing in a recognized toxicology model such as healthy cynomolgus monkeys. The Company has conducted studies of STRO-001 and STRO-002 in cynomolgus monkeys, and has revised pages 109 and 113 to provide additional detail about the toxicity findings in those studies, as requested in comment 8.

With regards to the date(s) of the studies, sponsor and location, given that these studies are non-human, preclinical studies conducted by the Company in its laboratories as is standard with non-human, preclinical studies, the Company believes that such information is not relevant. Additionally, the Company notes that size, dosage, duration and actual results observed are described in the text and in the graphics on pages 107, 108, 109, 112 and 113. While these studies have been presented at various conferences, the data has not been published in peer-reviewed journals.

In response to the Staff’s comment, the Company has revised its disclosure on pages 109 and 113 of Draft No. 2.

Collaboration and License Agreements, page 112

Celgene Collaboration, page 112

In response to the Staff’s comment, the Company has revised its disclosure on pages 81, 115 and F-21 of Draft No. 2.

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U.S. Securities and Exchange Commission

July 10, 2018

Page 5

Merck KGaA, Darmstadt, Germany Collaboration, page 113

The Company advises the Staff that it is not possible to disclose the precise years or range of years in which the MDA Agreement will expire because the term of the MDA Agreement is based on the later of the expiration of the patents covering products licensed under the MDA Agreement or ten years after the first commercial sale of a product covered under the MDA Agreement. Given the products are in an early stage of development, it is not currently possible to estimate when the first commercial sale of a product covered under the MDA Agreement will occur. Additionally, while the expiration date of patents currently covering products licensed under the MDA Agreement is known, these patents could be extended and new patents could be granted, which could significantly change the length of patent protection for the licensed products, which in turn would significantly expand the term of the MDA Agreement. While the Company could provide the earliest possible range of dates that the patents could expire, the Company respectively advises the Staff that the Company does not believe this information provides meaningful disclosure to potential investors since the disclosure represents only a current estimate. Moreover, the Company believes that this information may be misleading to potential investors since any new patent applications related to the MDA Agreement filed by the Company in the future would extend the term of the MDA Agreement, as would a first commercial sale occurring after such date. Thus, depending on the timing and extent of future patent applications filed by the Company and the timing of the first commercial sale of a product, any disclosure based on the current, earliest possible range in which the MDA Agreement will expire could significantly understate the actual term of the MDA Agreement.

Intellectual Property, page 116

In response to the Staff’s comment, the Company has revised its disclosure on page 120 of Draft No. 2.

Management, page 131

In response to the Staff’s comment, the Company has revised its disclosure on page 140 of Draft No. 2 to describe the role or function of its scientific advisory board and its clinical advisory board, as well as how members of such boards are compensated. The Company advises the Staff that the Company’s scientific and clinical advisory boards do not operate under any governance charters or formal rules of procedure.

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U.S. Securities and Exchange Commission

July 10, 2018

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Certain Relationships and Related Party Transactions, page 150

Letter Agreement with Four Oaks, page 151

In response to the Staff’s comment, the Company has revised its disclosure on page 154 of Draft No. 2.

The Company advises the Staff that the Company’s letter agreement with Four Oaks was made in the ordinary course of business and was terminated in October 2013. Furthermore, the payments to Four Oaks, though sufficient to require disclosure under Item 404 of Regulation S-K, amounted to less than 1.2% of the Company’s revenues in each of fiscal year 2015, 2016 and 2017. Moreover, while Four Oaks’ involvement facilitated the Company’s introduction to and initial collaboration with Celgene, the Company advises the Staff that Four Oaks’ involvement is not necessary for the continued collaboration between the Company and Celgene. The Company and Celgene have a strong relationship and a history of collaboration dating back to an initial collaboration in December 2012. Therefore, the Company advises the Staff that the letter agreement was both immaterial in amount and significance and was not an agreement upon which the Company’s business is substantially dependent. For these reasons, the Company respectively advises the Staff that the letter agreement does not need to be filed as an exhibit under Item 601(b)(10)(ii).

Principal Stockholders, page 153

In response to the Staff’s comment, the Company has revised its disclosure on page 158 of Draft No. 2.

General

The Company advises the Staff that neither the Company, nor anyone authorized on behalf of the Company, has provided written communications in reliance on Section 5(d) of the Securities Act of 1933, as amended, to potential investors. To the extent that any written communications may in the future be presented to potential investors, the Company will provide the Staff with copies of any such written communications.

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July 10, 2018

Page 7

The Company does not currently intend to include any additional graphic, visual or photographic information in the prospectus. However, if and to the extent that additional artwork or graphics are to be included, the Company will promptly provide such material to the Staff on a supplemental basis. The Company acknowledges that the Staff may have further comments on these materials once they are provided.

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Page 8

Should the Staff have additional questions or comments regarding the foregoing, please do not hesitate to contact the undersigned at (650) 335-7292, or, in his absence, Amanda Rose at (206) 389-4553.

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