According to the high prevalence of sexual disorders, this study was performed to determine the effects of pelvic floor muscle training on sexual function in postpartum women. A pragmatic, multi-center, single-blind, non-inferiority randomized controlled trial (RCT), women with sexual dysfunction at 3 to 6 months postpartum were divided into two groups: the pelvic floor muscle training intervention for two sessions, once a week for two hours (n = 40), and the postpartum usual care (PUC) group (n = 40), who was referred to healthcare centers in Babol from December 2020 to May 2021. They were randomly assigned to the two groups. Demographic information and the Female Sexual Function Index (FSFI) were used. After 8 weeks, all participants completed the FSFI again. Data were analyzed using an analysis of covariance (ANCOVA), with p ≤ 0.05 considered significant. There were no significant differences in baseline characteristics and pre-intervention FSFI scores. But after 8 weeks, the FSFI total scores (p = 0.001) and the scores of subscales such as desire (p = 0.001), arousal (p < 0.001), orgasm (p = 0.009), and satisfaction (p = 0.004) were significantly higher in the intervention group than in the PUC group. Pelvic floor muscle training can improve a woman’s sexual function after childbirth.