Background: The population of older women is rapidly increasing in every country in the world, including Iran. Given the effect of Sexual Function (SF) and sexual health on older women’s health, the present study was conducted to determine Sexual Dysfunction (SD) and the factors predicting it in Iranian older women in Karaj. Methods: The present cross-sectional study was conducted on 550 eligible older women selected by stratified cluster sampling from those visiting health centers in Karaj between October 2019 and February 2020. Data were collected using self-report questionnaires including demographic questionnaire, the hospital anxiety and depression scale (HADS), and the Female Sexual Function Index (FSFI). To take account of the effect of sampling design on the analyses, survey command in Stata-14 was used. Results: A total of 94.5% of the participating women had SD, 74.4% reported desire disorder, 79.8% arousal disorder, 57.6% lubrication disorder, 65.3% orgasm disorder, and 72.2% sexual dissatisfaction, and 52.4% had dyspareunia. The participating women’s SF had significant relationships with physical activity, hysterectomy, spouse’s SD, and the intimate and emotional closeness with the spouse (P<0.05). SF had significant inverse relationships with age, duration of marriage and menopause, anxiety, and depression (P<0.001). Nonetheless, SF had no significant relationship with occupation, education, smoking, and type and frequency of childbirth. The results of the linear regression test showed that the duration of menopause (B=-0.04, P=0.023), spouse’s SD (B=-0.95, P<0.001), intimacy (B=13.89, P<0.001), emotional closeness (B=6.49, P<0.001), anxiety (B=-0.08, P=0.033), and depression (B=-0.24, P<0.001) predicted the participating women’s SF significantly. Conclusion: The majority of the participating women had SD. Attention mental health, spousal relationship, and spouse’s sexual health may have significant positive effects on the sexual health of Iranian older women.