Abstract: Objective To evaluate AIDS related knowledge,high risk sexual behavior and physical condition in floating population in Hangzhou city.Methods Stratified multi-stage cluster sampling was adopted to select four types of floating population from Jianggan,Gongshu and Xihu district in Hangzhou city for a questionnaire survey.Results The most common way for floating persons to leave their home towns for a job was through introduction by their villagers(45.1%) or on their free will.The floating population had high mobility,with the median rate of mobility of inter-city,inter-trade,and inter-unit of 0.40/year,0.33/year,and 0.50/year,respectively.Among the population,the awareness rate of AIDS knowledge was 63.8% and there were statistically significant differences in the awareness rate among different occupational populations(χ²=22.5,P<0.001).In the floating population,the proportion of having temporary and commercial sexual experience was 5.5% and 4.4%.For the floating persons having temporary and commercial sexual experience,the rate of condom use in every sexual experience was 30.3% and 40.4%,the rate of no condom use was 12.8% and 9.6%,and the rate of condom use in the latest sexual experience was 47.7% and 65.4%.Conclusion Floating population in Hangzhou city had high mobility,low awareness of AIDS,and rare condom use in high risk sexual behavior.