Abstract: Objective To investigate the prevalence and risk factors of human immunodeficiency virus(HIV)and syphilis infection among older female sex workers(OFSWs)in Qingdao city,China and to provide evidences for making prevention and intervention strategies.Methods Totally 420 women aged ≥35 years,residing in Qingdao city at least 3 months,and having one or more commercial sex behavior during the previous one month were recruited with respondent-driven sampling(RDS) method between March and May 2014.The participants were surveyed with a questionnaire face-to-face and serum test for HIV and syphilis infection.Results A statistics verified representative sample of OFSWs was recruited and the average age of the participants was 42.6±6.4 years; most of the participants were Han ethnic,divorced or widowed,without local census register,and with the primary school or lower education.No HIV positive cases was identified among the participants.Among participants,125 had prior and 36 had current syphilis infection; the RDS-adjusted lifetime prevalence of syphilis was 31.8% and the active prevalence of syphilis was 9.1%.The result of multivariate logistic stepwise regression showed that with local census register(odds ratioOR=2.082,95% confidence interval95%CI=1.310-3.310),drug-use behavior(OR=2.006,95%CI=1.161-3.466),having commercial sex after the age of 35 years(OR=1.779,95%CI=1.133-2.791),and with a duration of commercial sex over 4 years(OR=1.930,95%CI=1.100-3.384) were factors related to the lifetime syphilis infection among the participants.Conclusion The serum prevalence of syphilis infection is high,suggesting an increased risk of HIV transmission among OFSWs in Qingdao city.