Objectives The purpose of the study was to investigate the incidence of HIV and syphilis and their related factors, as well as to examine the predictors associated with seroconversion among migrant men who have sex with men (MSM) in Beijing, China.

Design Prospective cohort study.

Setting Beijing, China.

Participants 511 HIV-negative migrant MSM.

Primary and secondary outcome measures Sociodemographic and behavioural information of participants, HIV and syphilis incidence rates, and factors associated with HIV/syphilis seroconversion and cohort retention.

Results Of the 511 participants, 60.3% (308) and 52.4% (273) were retained at the 4- and 8-month follow-up visits, respectively. The HIV and syphilis incidence rates were 7.83 (95% CI 4.48 to 12.72) and 11.11 (95% CI 6.47 to 17.80) per 100 person-years, respectively. HIV seroconversion was significantly associated with ‘had first anal intercourse at age 15 or younger’ (adjusted HR (aHR) 9.20, 95% CI 1.94 to 43.56) and ‘ever had group sex’ (aHR 4.30, 95% CI 1.40 to 13.18). Bisexual orientation (aHR 5.09, 95% CI 1.02 to 25.57) was significantly associated with syphilis seroconversion. Predictors associated with both 4- and 8-month retention rates included age ≥25 years old and living in Beijing for more than 1 year.

Conclusions The high incidence of HIV and syphilis among migrant MSM is a cause for concern. A comprehensive strategy should be implemented to maintain a higher retention rate among migrant MSM.