Regulation of seasonality in reproduction is closely related to melatonin and circadian rhythms. Melatonin affects the functions of reproductive organs through membrane melatonin receptors MT1 and MT2. The current knowledge about the presence, location and function of MT1 and MT2 receptors in the reproductive tract of an adult male European bison, seasonally breeding animal, is still missing. Frequently occurring organ in the male reproductive system of the European bison is uterus masculinus, what seems to confirm its specific role in seasonal reproduction control. Taking this into account, our study aimed to evaluate the expression of mRNA and protein synthesis for both melatonin receptors in the tissues of uterus masculinus in November and December in European bison. Protein synthesis of MT1 and MT2 receptors in uterus masculinus of mature European bisons was clearly raised in November and decreased in December. The comparable results were also found for mRNA expression of MT1 and MT2 receptors, where in November the expression level was significantly higher than in December. Therefore, we suggest that melatonin is needed in the European bison's reproductive system after a period of intensive reproductive activity in November. Probably, melatonin plays a protective function in uterus masculinus of the European bison and thus regulates the seasonal reproduction.