The expanding ageing population increases the importance of understanding frailty and related impacts on health. Our objectives were to examine the sexual function and its association with frailty among sexually active older adults aged 50+ living with HIV (OALHIV). A multi-centre cross-sectional study was conducted between September 2021 and July 2022. We enrolled OALHIV from specialized infectious disease hospitals providing HIV care in four cities in China. Data were collected through an investigator-administered questionnaire. Logistic regression was used to assess correlates of lower sexual function. 239 sexually active OALHIV (40 women and 199 men) were included in the present analyzes. 53 (22.2%) participants had frailty. About two-fifths (37.7%) reported at least one sexual difficulty lasting 3 months or more in the past year. Lack of interest in having sex was the most commonly reported sexual response problem (27.2%). 29.7% expressed satisfaction with their sex life. 49 participants were categorized as having a low sexual function. Frailty (aOR 3.03, 95%CI 1.22-7.53) was associated with low sexual function. OALHIV with frailty should be screened for sexual function problems. More efforts should be made to integrate sexual health services into geriatric services, ensuring comprehensive care that addresses their specific sexual concerns.