Abstract: Objective To study the loneliness among men who have sex with men(MSM) and to explore the relationship between feeling lonely and having multiple sex partners. Methods A cross-sectional study using snowball sampling techniques was conducted among 264 MSM in Shanghai from March 2015 to June 2015. Socio-demographic information, number of sexual partners, evaluation of the sense of loneliness were collected by questionnaires. Results The proportion of loneliness was 17.4%, and that of multiple sex partners was 52.7%. Univariate as well as multivariate logistic regression analysis showed non-local household registration (OR=2.08, 95%CI:1.20-3.63), and high lonely sense (OR=2.00, 95%CI:1.01-3.94) were risk factors for multiple sexual partners behavior. Conclusion Attention should be paid to loneliness problem during the behavior intervention among MSM.