BACKGROUND: Nowadays, infertility is one of the major problems of human societies. OBJECTIVES: To study oral administration of bulk milk and milk of late pregnant cows on spermatogenesis of male rats. METHODS: The first group of rats from day 1 of pregnancy until the end of lactation and then their male pups to maturity were treated with late pregnant cow’s milk. The second group from day 12 of pregnancy up to 15 days after delivery was treated with late pregnant cow’s milk. The third group of rats from day 1 of pregnancy until the end of lactation and then their male pups to maturity were treated with bulk milk. The fourth group from day 12 of pregnancy up to 15 days after delivery was treated with bulk milk. Rats in the control group during the study period were only fed with special food of rats and at the end viability, types of movement (progressive and in-place movement, immobility), number of sperms and also the serum testosterone level were elevated. RESULTS: Administration of both types of milk had no effect on in-place movement and also viability of sperms of experimental groups but they could cause a significant increase in sperm  immobility and a significant decrease in number of sperms of experimental groups. Also,the level of serum testosterone of experimental groups was significantly reduced in comparison with control group (p<0.05). CONCLUSIONS: Overall, it was determined consumption of late pregnant cow’s milk and bulk milk when it contains high estrogen can cause changes in some sperm species that are involved in male reproduction.