Objective:To investigate the prevalence and risk factors for syphilis among men who have sex with men (MSM) in Nanjing. Methods:A face-face questionnaire interview was conducted among MSM by snowball sampling method in Nanjing from March to July,2009. Socio-demographic,behavioral and other characteristics were included in the questionnaire. Bivariate and multivariate logistic regression model was constructed to evaluate independent factor associated with syphilis. Results:A total of 661 MSM were recruited. The mean age of these participants was 27.44 years. Among them 84.0% were unmarried,and 90.5% had an education beyond senior middle school; in the past 6 months,5.0% had sexual contact with more than 10 male sex partners,the rate of protected anal sex during the past 6 months was 36.0%. The percentage of people who had ever paid for male sex service was 3.9%,who had provided commercial sex service to male was 4.5%,and who had sexual contact with female was 21.0%. Syphilis was diagnosed in 11.5% of these participants,the risk factors independently associated with syphilis clude being older than 25 years (adjusted OR=4.20,95%CI:2.26~7.80),non-local residency(adjusted OR=1.67,95%CI:1.00~2.78),looking for male sex partners from bathhouse(adjusted OR=2.29,95%CI:1.26~4.15),sexually transmitted diseases examination and treatment in 1 year before interview(adjusted OR=2.15,95%CI:1.25~3.69). Conclusion:The rate of unprotected anal sex was high, so was the prevalence of syphilis among MSM. Further efforts are urgently needed to scale-up the prevention of syphilis among MSM.