Abstract: ObjectiveTo understand the incidence of extramarrital sexual intercourse,the rate of condom use and its influencing factors among floating population and provide basis for promoting condom use.Methods975 migrants in Baotou city,Inner Mongolia Autonomous Region were anonymously investigated with questionnaires by using the target populations geographical distribution map and randomly cluster sampling method.ResultsBased on the data of 965 effective questionnaires,the rate of extramarrital sexual intercourse was 1011%,and the rate of condom use was 36.4% in commercial sexual intercouse and 26.7% in casual partener sexual intercouse respectively.It was not found that the rate of condom use was related to subjects'gender,educational level,jobs,HIV/AIDS related knowledge and the attitude towards AIDS patients.ConclusionThe rate of condom use is low and shows that condom use are not paid enough attention to among floating population during extramarrital sexual intercourse.It is very hard to prevent sexual transmitted diseases and AIDS with such a low rate of condom use.So it is imperative to explore further measures of promoting condom use.