Abstract: Objective To understand the positive seroconversion of human immunodeficiency virus(HIV) and Treponema pallidum antibodies among men who have sex with men(MSM) in Hangzhou. Methods MSM were recruited from HIV voluntary counsel and test(VCT) clinics in 5 districts in Hangzhou, and follow up for 3 and 6 months was made among them to learn about their high risk behaviors. Blood samples were taken from them to detect the antibodies to HIV and Treponema pallidum. Results Among 80 HIV negative MSM recruited, 3.75%(3/80) were Treponema pallidum positive, 92.5%(74/80) completed the 6 month follow up. The positive seroconversion rates of HIV and Treponema pallidum antibodies were 10.7/100 person-years and 13.9/100 person-years respectively. Conclusion The positive seroconversion of HIV and Treponema pallidum in this MSM cohort was very serious. More effective measures should be taken to reduce the prevalence of HIV infection and syphilis in MSM in Hangzhou.