Unprotected sexual transmission is the cause of approximately 70%–80% of human immunodeficiency virus (HIV) infections worldwide. Prevalence of HIV infection in 2011 was more than ten fold higher (3.8%) among men who have sex with men (MSM) than in the general population (0.33%) in Nepal. This study aimed to explore sexual behaviors, and social and demographic characteristics of MSM in Kathmandu Valley, Nepal. A quantitative cross sectional study was conducted among 113 MSM. MSM is a hidden population in Nepalese society, therefore, it was difficult to construct a sample frame for this research so, respondent driven sampling was used which gives unbiased estimates of population parameters and has the potential to reach MSM, who are not easily accessible. A structured interview was used to obtain the information. The majority of respondents were above 20 years old (mean = 27.9 years, SD = 7.4 years). Most respondents were receptive, 43.4% identified themselves as Meti. Forty six percent of respondents were married. The majority had sex with males which was predominantly anal. MSM had an average number of 74 sex partners (last three months). Nearly 95% had used a condom, and 92% had used lubricant during their last sex act. Thirty eight percent perceived themselves as at risk of HIV. The majority knew of a place for confidential HIV testing in Kathmandu. This study highlights the importance of partner tracing during HIV counseling and testing, the importance of drop-in centers to increase access to condoms, and supports the need to increase comprehensive health services and peer led participatory behavioral change communication activities to this population in the national HIV response.