Abstract: Objective To examine new syphilis infection and its influencing factors among men who have sex with men(MSM) in Mianyang city.Methods Respondent driven sampling was used to recruit MSM in Mianyang city from June to September 2009 and an open prospective cohort was established.Serological follow-up survey was conducted once a year for three consecutive years.Snowball sampling method was adopted to recruit MSM for the supplement of participants lost to follow-up.Results During the study period, 583 MSM were included in the cohort, with a total of 535.5 person-years of follow-up.Totally 30 new-syphilis infections were diagnosed and the new infection rate was 5.6/100 person-years(95% confidence interval95%CI: 3.7-7.6/100 person-years).Multivariate analyses showed that the influencing factors of new syphilis infection included marital status(relative riskRR=2.377, 95%CI:1.035-5.459), knowledge about AIDS(RR=4.278, 95%CI: 1.941-9.431), with peer education during last one year(RR=2.281, 95%CI: 1.081-4.815), and being diagnosed with sexually transmitted diseases(RR=4.743, 95%CI: 1.829-12.302).Conclusion New syphilis infection is relatively stable in local MSM population but still higher and affected by marital status, knowledge about AIDS, peer education and infections of STDs.