The purpose of this study was to investigate the effect of regular moderate- to high-intensity step aerobics training on the melatonin levels and sleep quality of sleep-impaired postmenopausal women (PMW). PMW with poor sleep (having a score over 5 in the Chinese version of the Pittsburgh sleep quality index [PSQI]) were divided into a training group (TG, n = 10) and an age-, height-, weight-, and PSQI score-matched control group (CG, n = 9). The participants in the TG performed 40-45 minutes of step aerobics exercise 3 times per week for 10 weeks at an intensity of 75-85% of the heart rate reserve, whereas the participants in the CG maintained their regular lifestyle. The fasting blood was analyzed, and the PSQI questionnaire and aerobic fitness test were administered before and after the 10-week program. The results revealed that for the participants in the TG, the PSQI score significantly decreased (TG from 9.40 ± 0.81 to 7.40 ± 0.43; CG from 7.56 ± 0.34 to 7.78 ± 0.68; between-group difference = 2.22, p ≤ 0.05) and the melatonin levels significantly increased (TG from 12.08 ± 4.20 to 44.42 ± 7.03 pg·ml; CG from 11.81 ± 2.03 to 5.5 ± 1.39 pg·ml, between-group difference = 38.65, p ≤ 0.05). In conclusion, a 10-week moderate- to high-intensity step aerobics training program can improve sleep quality and increase the melatonin levels in sleep-impaired PMW. Therefore, regular moderate- to high-intensity step aerobics training is recommended for sleep-impaired PMW.