Abstract: Objective To examine different motivations for homosexual behavior and their associations with demographics,sexual behavior,and human immunodeficiency virus(HIV) infection of men who have sex with men(MSM) in Beijing.Methods With respondent-driven sampling(RDS),600 MSM living in Beijing were surveyed face-to-face with a questionnaire on demography,reasons for engaged in homosexual activity,and HIV infection related behaviors.Blood samples of the MSM were collected for HIV detection.Results Of all the MSM,65.5%(393,named innateness group) attributed their involvement in homosexual activity to innate tendency,33.5%(201,named curiosity group) to curiosity,and only 6(1.0%) to other motivations.The average age of the MSM was 32.8±9.2 years,and the average age of MSM of innateness group was significantly younger than that of curiosity group(P<0.05).The proportion of being unmarried was higher in innateness group than in curiosity group(74.8% vs.60.2%,P<0.05).The MSM of innateness group reported a higher education level than the curiosity group(P<0.05).The curiosity group reported a significantly higher ratio of bisexual behavior than innateness group(52.7% vs.19.6%,P<0.05).There were 38.9% of the MSM in curiosity group reporting the preference of having insertive anal sex,significantly higher that in innateness group(30.6%)(P<0.05),whereas,there were 71.2% of the MSM of innateness group reporting the preference of having a regular sexual partner,higher than those of curiosity group(62.5%).The proportion of having sex with females was significantly higher in the curiosity group than that in the innateness group(77.6% vs.38.4%,P<0.05).The MSM of curiosity group knew less AIDS related policy and knowledge and the sites of HIV voluntary counseling and testing than those of innateness group(all P<0.05),but the HIV positve rate was significantly higher in the MSM of curiosity group than those of innateness group(14.4% vs.8.1%,P<0.05).Conclusion Different motivations for the involvement in homosexual activity have different impacts on the risk of HIV transmission among MSM.The MSM of curiosity group,which have lower social status,poorer knowledge about safety sex,and higher HIV infection rates,may play an important role in the transmission of HIV.