Abstract: ObjectiveTo study the knowledge and behavior about human immuno-deficiency virus/acquired immunodeficiency syndrom(HIV/AIDS)and HIV infection among men who have sex with men(MSM)in Liaoning province, 2010.MethodsA cross-sectional anonymous questionnaires survey was carried out among 1 205 MSM living in Shenyang, Dalian,and Anshan city of Liaoning province.ResultsThe rate of HIV/AIDS knowledge was 91.2% .There were 80.58% of the MSM having sex with man,of which 46.04% had unprotected buggery during the last six months.There were 2.7% of the MSM had history of venereal diseases and there was a significant difference in the prevalence of venereal diseases between the MSM with non-commercial sexual behavior and commercial sexual behavior.There were 57 MSM being positive to HIV antibody with a HIV infection rate of 4.7% .ConclusionThe knowledge level related to HIV/AIDS was relatively high but the rate of high-risk sexual behaviors was also high in the MSM in Liaoning province.Effective intervention should be promoted among the MSM.