Abstract: Objective To explore the effect of conjugal relationship on spouse's seroconversion of human immunodeficiency virus (HIV)among HIV serodiscordant couples in Yunnan province.Methods Using case-control design,we conducted a retrospective questionnaire survey among 109 HIV sero-accordant spouses (case group) and 114 HIV sero-discordant couples (control group) recruited from 6 prefectures,33 counties or districts in Yunnan province between July 2014 and September 2015.The collected data were processed with Epi Data 3.1; χ² test and univariate analysis were conducted using SPSS 15.0.Results The proportion of reporting a good conjugal relation was significantly higher among the HIV positive participants of the control group than among those diagnosed before their spouses of the case group (71.93% vs.52.29%,P=0.0021);the proportion of reporting giving more concerns to their HIV positive spouses after the disclosure of test result was significantly higher among the HIV negative participants than among the participants with HIV positive conversion after their HIV positive spouses (30.97% vs.11.01%,P<0.001);the proportion of reporting carrying out discussions about how to prevent HIV transmission between couples with their spouses was significantly higher among HIV positive participants in the control group than among the those diagnosed as HIV positive before their spouses in the case group (76.79% vs.54.13%,P<0.001).The proportion of reporting having marital sex after the awareness of HIV positive status and the HIV test of their spouses were significantly lower among the controls than among the cases (P=0.013 and P=0.003);the proportion of reporting using condom during every marital sex after the awareness of HIV positive status was significantly higher among the HIV positive participants of the control group than among those of the case group (P<0.001).Conclusion Good conjugal relation,concerns to the HIV positive first diagnosed,communication on the prevention of HIV transmission between couples,control of marital sex,and condom use during every marital sex are protective factors for the prevention of HIV transmission among HIV serodiscordant couples.