This study was conducted to investigate the effects of melatonin implantation on basic testicular characteristics and reproductive performance of Kivircik and Charollais rams and ewes during the nonbreeding season. In this study, 8 Kivircik and 6 Charollais rams were used. Rams were implanted with 54 mg melatonin according to the manufacturer's instructions. At melatonin implantation and at ram introduction the reproductive performance and testicular characteristics were evaluated. Throughout the experimental period, rams were permanently kept outdoors under conditions of natural day length and at ambient temperature. The effects of exogenous melatonin treatments on the reproductive performances of rams and ewes, estrus response, pregnancy rate, litter size and twinning rate of ewes were evaluated in all groups. Libido values were significantly higher in Charollais rams compared to Kivircik rams (P< 0.001). Testicular volume (TV) was increased in both ram breeds. Scrotal length (SL) was also increased in both Kivircik and Charollais rams (P< 0.01). In conclusion, we showed that the treatment of rams with slow release melatonin implants increased scrotal diameters and testicular volumes in both Kivircik and Charollais rams. Furthermore, melatonin implantation improved the reproductive performances of ewes naturally mated with these melatonin implanted rams during non-breeding season.