Abstract： Background Resumption of menstrual cycles is one of the indicators for restoration of reproductive capability in postpartum women. However, menstruation does not necessarily mean that ovulation has taken place. The aim of this study was to investigate the relation of supplementary feeding to return of menstruation and ovulation after delivery.Methods A questionnaire was used to obtain data from 101 breastfeeding mothers. The following elements were analyzed: age, education level, breastfeeding practice, time of return of menstruation, contraceptive practice, and starting time of supplementary feeding during the lactation at intervals of 6 weeks to 18 months after delivery. The ovulation was continuously monitored by ultrasonography and basal body temperature (BBT) measurement.Results By ultrasonography, 53 of the 101 women (52.5%) had the first ovulation (follicle ＞1.8 cm in diameter)within 154 days after delivery on average, among whom 11 (10.9%, 11/101) had restoration of ovulation within 4 months and 42 (41.6%, 42/101) had it after 4 months. In women with follicles ＞1.8 cm in diameter (n=53), the menstruation resumed (138±84) days after delivery, and the supplementary feeding was started at (4.0±1.1) months, which were significantly earlier than those in the women with follicular diameter ＜1.7 cm (n=48; (293±88) days, (5.1±1.3) months; t=9.003,P＜0.01 and t=4.566, P＜0.01). In the women with follicles ＞1.8 cm in diameter, 30 had return of menstruation before the end of ultrasonographic monitoring, while only 8 in the women with follicular diameter ＜1.7 cm had menstrual resumption at the same time (x2=16.91, P＜0.01). The starting time of supplementary feeding was positively correlated with the time of the restoration of menstruation (n=100, r=0.4764, P＜0.01) and first ovulation after delivery (n=53, r=0.5554, P＜0.01).In this series, no woman had pregnancy within 18 months postpartum.Conclusion Supplementary feeding can affect the restoration of menstrual cycles and ovulation in lactating postpartum women.