Migrant men who have sex with men (MSM) may be particularly vulnerable to sexually transmitted infections (STIs) including HIV. This study examines the rates of HIV and syphilis infections and associated socio-demographic and behavioral factors among migrant MSM in China. Data from 307 migrant MSM were collected in Beijing, China. Blood specimens were collected to test for HIV and syphilis infections. HIV and syphilis rates were 5.9% and 20.2%, respectively. Multivariate logistic regression analyses showed that having ever been married, living a longer period in Beijing, having more sexual partners, and having a foreign MSM friend were significantly associated with HIV infection. Migrating from a rural area, experiencing one's sexual debut at an older age, having a male as first sexual partner, having more sexual partners, and being recruited from peer outreach and social network were associated with syphilis infection. Migrant MSM in China are at high risk for HIV and syphilis infections. HIV prevention programs targeting rural migrant MSM who have been married are needed.