Abstract: Objective To explore demographic characteristics,human immunodeficiency virus(HIV)high-risk behavior,and the prevalence and influencing factors of HIV and syphilis infections among men who have sex with men(MSM)in Changzhou city.Methods Questionnaire interviewwas conducted to collect information on demographic characteristics,behaviors of sex and drug use,HIV and sexually transmitted infections(STIs)related health services.Blood and urine samples were tested for HIV/syphilis antibodies and Neisseria gonorrhoeae(NG)and Chlamydia trachomatis(CT)infections.Results Of 593 participants,13.7%(81)were HIV-positive,31.2%(185) were sero-positive for syphilis infection,and 7.1%(42)were both HIV-positive and sero-positive for syphilis infection.There were 5.7%(34/592)of MSM having sexual abuse.In the latest 6 months,63.9%(379/592)of the MSM had anal sex with men,of which 24%(91/379)did not use condom in the recent anal sex.There were 47.2%(280/592)of the MSM having sex with women,of which 46.8%(131/280)did not use condom in the recent vaginal sex with women.Factors associated with HIV infection included age(χ²=14.83,P=0.005),occupation(χ²=11.06,P=0.047),sex abuse(odds ratioOR=2.97,95% confidence intervalCI1.26-7.01),syphilis infection(OR=3.17,95% CI:1.88-5.35).The risk of HIV infection for student MSM was three times of that in workers/migrant workers(OR=3.01,95% CI:1.04-8.72).Factors associated with HIV infection included positive for HIV infection(OR=10.60,95% CI:1.09-103.55)and bleeding in sex abuse(OR=11.95,95% CI:1.27-112.68).Conclusion The HIV-high risk sex behavior was prevalent among MSM population in Changzhou city and the prevalence rates of HIV and syphilis infection were high.Screening of HIV and STIs and normative treatment to the diseases are essential in the high risk population.