WASHINGTON—Mark Wu, the U.S. Trade Representative’s top China adviser, said he resigned his position, citing family reasons.

In an interview, Mr. Wu said he left USTR in mid-July and is returning in August to Harvard Law School where he focuses on intellectual property issues and Chinese trade policy.

“The plan had always been to help (Trade Representative) Katherine Tai settle into her role,” Mr. Wu said. “The team has settled into place, and a rhythm has been established.”

Mr. Wu cited family issues as another reason for his departure, which he said had nothing to do with the continuing USTR review of China policy.

U.S. Trade Representative Katherine Tai

U.S. Trade Representative Katherine Tai

Photo: Susan Walsh/Press Pool

USTR is in the midst of a broad review of its China policy, which is expected to be completed in the fall. Few details of the policy have been made public, leading to mounting frustration by big investors and exporters to China. Mr. Wu declined to comment on the policy effort.

Sarah Bianchi, a onetime classmate of Mr. Wu’s at Harvard, is awaiting confirmation by the full Senate as deputy U.S. Trade Representative with responsibility for China and the rest of Asia.

Write to Bob Davis at bob.davis@wsj.com