Abstract: Objective To examine unprotected commercial sexual behavior and its influencing factors among middle and low income female sex workers(FSWs) in Kunming city and to provide advice for developing comprehensive human immunodeficiency virus/acquired immunodeficiency syndrome(HIV/AIDS) prevention and treatment among FSWs.Methods Totally 561 FSWs with middle and low income from 4 districts of Kunming city were surveyed with a self-designed questionnaire.Logistic regression model was used to analyze influencing factors of unsafe sexual behavior.Results Among the FSWs,58.1% had unprotected sexual behaviors in the latest 3 months.Factors significantly related to unprotected sexual behavior were age(P=0.000),monthly income(P=0.044),duration of sex work(P=0.001),care for health or not(P=0.000),the disease most worried about(P=0.000),experience of occupational abuse(P=0.016),score of AIDS knowledge(P=0.010),place of sexual service(P=0.000),and average working days in a month(P=0.000).Multivariate logistic regression showed that age(odds ratiioOR=0.470,95% confidence intervalCI:0.313-0.704),care for health or not(OR=4.249,95%CI:2.680-6.735),the disease most worried about(OR=0.231,95%CI:0.090-0.591),score of AIDS knowledge(OR=2.371,95%CI:1.400-4.014),place of sexual service(OR=0.852,95%CI:0.728-0.998),and average working days in a month(OR=1.755,95%CI:1.099-2.801) were associated with the unsafe sexual behavior.Conclusion Unprotected commercial sexual behaviors among FSWs with middle and low income are influenced by the age,health attitude,duration of the work,place of sexual service,average working days in a month,and the experience of occupational abuse.