Abstract: ObjectiveTo examine the prevalence and influence factors of human immunodeficiency virus (HIV)-syphilis co-infection in Ningbo municipality,Zhejiang province and to provide references for conducting corresponding interventions.MethodsA cross-sectional study was performed at HIV voluntary counseling and testing (VCT) clinics in Ningbo municipality from May to December,2015.A total of 2 090 registered adult HIV infected persons were recruited.Electronic questionnaire and Ningbo acquired immunodeficiency syndrome (AIDS)special management registration software were used to collect data on socio-demography and potential risk factors for syphilis infection.ResultsThe prevalence rate of syphilis sero-positive was 9.4% in the participants.The influence factors for HIV-syphilis co-infection included gender,age,education level,the number of sexual partners and whether having highly active antiretroviral therapy (HAART);the risk factors were having more than 2 sexual partners and at the age of 46 years or older,while the protective factors were female gender,with higher education,and having HAART.ConclusionThe prevalence of syphilis is high and gender,age,education level,number of sexual partners,and whether having HAART are main influence factors of syphilis infection among the people infected with HIV in Ningbo municipality.