UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13A-16 OR 15D-16

OF THE SECURITIES EXCHANGE ACT OF 1934

For the month of September 2018

Commission Filing Number: 001-38205

ZAI LAB LIMITED

(Translation of registrant’s name into English)

4560 Jinke Road, Bldg. 1, 4F, Pudong, Shanghai, China 201210

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F: Form 20-F  ☒ Form 40-F  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ☐

EXHIBIT INDEX

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: September 4, 2018

Exhibit 99.1

Zai Lab Announces Proposed Public Offering of American Depositary Shares

SHANGHAI, China, September 3, 2018 (GLOBE NEWSWIRE) – Zai Lab Limited (“Zai Lab” or the “Company”) (NASDAQ:ZLAB), a Shanghai-based innovative biopharmaceutical company, today announced that it has commenced an underwritten public offering of $150,000,000 of American Depositary Shares (“ADSs”) representing ordinary shares of the Company. All ADSs will be offered by Zai Lab. In addition, Zai Lab expects to grant the underwriters a 30-day option to purchase up to $22,500,000 of additional ADSs.

J.P. Morgan, Citigroup, Jefferies and Leerink Partners are acting as joint book-running managers for the offering. The offering is subject to market and other conditions, and there can be no assurance as to whether or when the offering may be completed.

A registration statement on Form F-1 relating to the securities proposed to be sold in this offering has been filed with the U.S. Securities and Exchange Commission but has not yet become effective. These securities may not be sold nor may offers to buy the securities be accepted prior to the time that the registration statement becomes effective.

This offering is being made only by means of a prospectus. Copies of the preliminary prospectus may be obtained from: (i) J.P. Morgan Securities LLC, Attention: Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, telephone: 1-866-803-9204 or email: prospectus-eq_fi@jpmchase.com, (ii) Citigroup Global Markets Inc., c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717 or telephone: 1-800-831-9146 (iii) Jefferies LLC, Attention: Equity Syndicate Prospectus Department, 520 Madison Avenue, 2nd Floor, New York, NY 10022, by telephone at 1-877-821-7388, or by email at Prospectus_Department@jefferies.com or (iv) Leerink Partners LLC, Attention: Syndicate Department, One Federal Street, 37th Floor, Boston, MA 02110, telephone: 1-800-808-7525 ex. 6132 or email: syndicate@leerink.com.

This press release does not constitute an offer to sell or the solicitation of an offer to buy ADSs or any other securities, nor shall there be any sale of ADSs in any state or jurisdiction in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Zai Lab

Zai Lab (NASDAQ:ZLAB) is a Shanghai-based innovative biopharmaceutical company focused on bringing transformative medicines for cancer, infectious and autoimmune diseases to patients in China and around the world. The company’s experienced team has secured partnerships with leading global biopharma companies, generating a broad pipeline of innovative drug candidates targeting the fast-growing segments of China’s pharmaceutical market and addressing unmet medical needs. Zai Lab’s vision is to become a fully integrated biopharmaceutical company, discovering, developing, manufacturing and commercializing its partners’ and its own products in order to impact human health worldwide.

Zai Lab Forward-Looking Statements

This press release includes certain disclosures which contain “forward-looking statements.” You can identify forward-looking statements because they contain words such as “anticipate” and “expected.”

Forward-looking statements are based on Zai Lab’s current expectations and assumptions. Because forward-looking statements relate to the future, they are subject to inherent uncertainties, risks and changes in circumstances that may differ materially from those contemplated by the forward-looking statements, which are neither statements of historical fact nor guarantees or assurances of future performance. Important factors that could cause actual results to differ materially from those in the forward-looking statements are set forth in Zai Lab’s Annual Report on Form 20-F for the fiscal year ended December 31, 2017 and its other filings with the U.S. Securities and Exchange Commission. Zai Lab undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as may be required by law.

ZAI LAB CONTACTS:

Zai Lab

Billy Cho

+86 21 6163 7322

billy.cho@zailaboratory.com

Media: Nancie Steinberg & Robert Flamm

Burns McClellan, on behalf of Zai Lab

212-213-0006, ext. 318, nsteinberg@burnsmc.com

212-213-0006, ext. 364, rflamm@burnsmc.com

Investors: Jill Steier

Burns McClellan, on behalf of Zai Lab

212-213-0006, ext. 364, jsteier@burnsmc.com