In this study, the effects of melatonin (MT) on superovulation and reproductive hormones (melatonin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and PRL) were investigated in female sika deer. Different doses (40 or 80 mg/animal) of melatonin were subcutaneously implanted into deer before the breeding season. Exogenous melatonin administration significantly elevated the serum FSH levels at the time of insemination compared with levels in control animals. During superovulation, the serum LH levels in donor sika deer reached their highest values (7.1 +/- 2.04 ng/mL) at the point of insemination, compared with the baseline levels (4.98 +/- 0.07 ng/mL) in control animals. This high level of LH was sustained until the day of embryo recovery. In contrast, the serum levels of PRL in the 80 mg of melatonin-treated group were significantly lower than those of control deer. The average number of corpora lutea in melatonin-treated deer was significantly higher than that of the control (p < 0.05). The average number of embryos in the deer treated with 40 mg of melatonin was higher than that of the control; however, this increase did not reach significant difference (p > 0.05), which may be related to the relatively small sample size. In addition, embryonic development in melatonin-treated groups was delayed.