Background Sexual function is an important yet understudied aspect of overall health and well-being in older adults. We aimed to examine sexual function and its correlates among people 50 years and older in China. Methods We enrolled people aged 50 years and older recruited from four regions in China between September 2021 and July 2022 in a multicenter cross-sectional study. Data were collected through an investigator-administered questionnaire about demographic characteristics, health characteristics, and sexual function status. Logistic regression was used to assess correlates of lower sexual function (the highest quintile of the sex-specific population distribution of Natsal-SF scores [i.e., lower functioning compared with the remaining]). Results A total of 465 women and 832 men who were sexually active in the past years were included in the analysis (mean age: 60.4 ± 7.2). Over a quarter of all participants were dissatisfied with their sex life. Notably, 92 women and 167 men were categorized as having a lower sexual function. Age (in men only), living in urban areas, general health status, being underweight or overweight (in men only), and having depressive symptoms were associated with lower sexual function. Among all participants, 43.1% of men and 54.0% of women experienced sexual response problems lasting 3 months or more. Less than one-third of all participants had sought help or advice for sex life in the past year. Conclusions Sexual dysfunction and sexual dissatisfaction are prevalent among older adults in China and are associated with self-assessed poor health. More efforts are needed to better understand sexual health needs and tailor service provision.