Background and Objective: There is controversy on the psychological effects of postpartum exer- cise. The study aimed to evaluate the effective- ness of a postpartum exercise program on health- related quality of life and psychological well- being. Methods: We conducted a randomized controlled trial in Tokyo, Japan. The intervention groups participated in ball-exercise classes (week- ly exercise of 90 minutes for four weeks) at three months postpartum. The exercise class included the following: 1) greeting and warm-up; 2) aero- bic exercise involving bouncing on an exercise ball 55 or 65 cm in diameter; 3) rest and self- introduction; 4) stretching and cooling down. The primary outcome measure was health-relat- ed Quality of Life (QOL) assessed using the MOS Short-Form 36-Item Health Survey (SF-36v2). The secondary outcome measures were Rosen- berg Self-Esteem Scale (RSES) and Edinburgh Postnatal Depression Scale (EPDS) scores. The intervention group was compared to the control group at four months postpartum. Results: Of the 120 women screened, 110 women met the study criteria. Nine could not be included and the remaining 101 were allocated randomly into intervention and control groups (50 and 51 par- ticipants respectively). Analysis of covariance adjusting for baseline values indicated that the SF36 subscales of physical functioning (p = 0.018) and vitality (p = 0.016) significantly im- proved in the intervention group compared to the control group, although there were no signi- ficant differences between the groups in the SF36 Physical Component Summary (PCS) and Mental Component Summary (MCS) scores. The RSES increased in the intervention group (p = 0.020) compared to the control group. No signi- ficant group differences were observed in EPDS scores. Conclusions: The postpartum exercise class program provided to healthy postpartum women appears to have contributed to promo- ting health-related QOL and self-esteem.