ObjectivesTo investigate sexual behaviours among HIV-discordant heterosexual couples and assess the correlates of condom use at the couple level.DesignCross-sectional study.SettingSeven prefectures along the Yangtze River in the Anhui Province, China.ParticipantsWe included 412 participants aged 18 years or older (206 married HIV-discordant couples).Primary and secondary outcome measuresIn this study, sexual behaviours included marital or extramarital sex in the past 6 months, as well as the frequency of marital sex and condom use (always, sometimes or never) if having marital sex in the past 6 months. We used stepwise ordinal logistic regression modelling to determine the correlates of condom use.ResultsIn total, 63.1% (130 of 206) of couples had marital sex in the past 6 months, of which 89.2% (116 of 130) used condoms consistently. Couples with more marital duration (OR=1.15; 95% CI: 1.03, 1.28) were more inclined to adhere to condom use, whereas those lacking support and care (OR=0.25; 95% CI: 0.07, 0.94) and being remarried (OR=0.08; 95% CI: 0.02, 0.43) were associated with less condom use. In addition, HIV-positive respondents were more likely to have extramarital sex than HIV-negative respondents (p=0.015).ConclusionsThe extramarital sex of HIV-positive spouses should be considered. Implementation of interventions, such as increasing support and care between spouses to promote marital intimacy and stability, could reduce unprotected sexual behaviour.