Tsinghua University and Peking University became the biggest sources of doctoral students in the US in recent years, according to a report on migration published on Monday.

The School of Law at the Beijing Institute of Technology and the Center for China and Globalization (CCG) jointly issued the Annual Report on Chinese International Migration (2012) on Monday, the Beijing News reported Tuesday.

According to the report, Tsinghua University sent 571 doctoral students and Peking University sent 507 doctoral students to the US in 2006. Since then the two schools have topped US universities in terms of providing doctoral students.

However, most of these Chinese overseas students did not return to China after receiving their diplomas. Chinese students occupied 92 percent of foreign students who earned science and engineering doctorates in 2002 and remained in the US as of 2007.

The report also says that China sends more students overseas than any country.

Wang Huiyao, director of the CCG and editor of the report, said that in 2011, 36.5 percent of overseas students returned to China after graduating.

"Comparing with the students going abroad, returning students are still few," Wang said, noting that the international average return rate is about 50 to 60 percent.

The Beijing News