Abstract: Objective To examine heterosexual behavior and its influencing factors among men who have sex with men(MSM).Methods With respondent-driven sampling (RDS),self-administered anonymous questionnaire survey was conducted among 400 MSM in Miaryang city,Sichuan province during June to Sepeember,2009.Results Among the MSM,142(35.5%) had their first sex with women and 73(18.3%) had sex with women in the latest 6 months,whit an average nubmer of partner of 1±2.42.For the 73 MSM having sex with women,13 had sex with their wives,29 with their girlfriends,and 3 with female sex workers and 35(47.9%) used condom in the last sex,23(30.1%) used condom in sex behavior during the latest 6 months.Multivariate unconditional logistic regressions showed that education level,marriage status,sexual orientation,household register,partner of first sex,frequency of city transient of the sex partner,and having comecial sex with male in the latest 6 months were main influencing factors of heterosexual behaviors among the MSM (χ²=4.970,0.455,15.419,8628,11.759,7.379,and 5.335; P< 0.05 or P< 0.01 for all).The MSM with education low er than senior high school,married,bisexual,having their first sex with women,w ith the sex partner having more than 2 times of city transient,having sex with male in the latest 6 months,and with local household registration were more likely to have heterosexual behavior.Conclusion A large number of MSM have heterosexual behaviors and and the behaviors are influenced by demographic factors,partners of the first sex,and city transient.The MSM with heterosexual behavior are key groups for AIDS control.