Abstract: Objective To investigate the knowledge about acquired immunodeficiency syndrome(AIDS),high-risk behavior,AIDS/sexually transmitted disease (STD) infection and related factors among migrant population in Beijing city.Methods Betw een June and December in 2009,multiple sampling methods were adopted to select migrant builders,migrant laborers in industrial and commercial sectors in Beijing city.The subjects were investigated with a structured face-to-face questionnaire interview and detected for human immunodeficiency virus (HIV),syphilis and hepatitis C infection.Results A total of 4 187 migrants were recruited and surveyed.The prevalence rate of HIV,syphilis and hepatitis C virus(HCV) infection among the subjects was 0.0% (0/4 187),0.4% (15/4 187),and 0.6% (25/4 187),respectively.The aw areness rate of know ledge about AIDS was 63.9% (2 677/4 187) and 75.9% (3 144/4 141) of the respondents had sex experience.There were 4.3% (177/4 141) of the subjects having sex with noncommercial casual partners in the previous one year,of which 27.1% (48/177) having no condom use while 29.4% (52/177) using condom in every sex.Age,marital status,educational level,time living in Beijing,and occupation were independent predictors of the awareness of knowledge about AIDS.Gender,marital status and time living in the city were independently associated with the causal sexual activity among the migrant population.Conclusion Education and intervention measures must be strengthened to prevent the transmission of AIDS/STD in migrant population in Beijing city.