Mancozeb, a fungicide of ethylenebisdithiocarbamate group was orally administered at 800 mg/kg body weight to male Swiss albino mice for 5, 10, 20 and 30 days. Daily body weight of the mice were recorded. The mice were sacrificed by cervical dislocation after 24 h of terminal exposure of mancozeb. Testes weight decreased significantly in 20 and 30 days mancozeb treated mice. However, there was a significant decrease in the number of spermatogonia, diameter of spermatocytes and spermatids in 20 days and number of spermatids in 10 days mancozeb treated mice. Histologic studies of the testis of the mice treated with mancozeb for long duration revealed spermatogenesis inhibition reflected by significant decrease in the number of spermatogenic cells and sperms, when compared with that of controls. In the mice treated with mancozeb for 20 and 30 days showed significant decrease in the weight of the prostate gland. However weight of Cowper's glands decreased significantly in 30 days mancozeb treated mice. There was significant decrease in the kidney, spleen and liver weight, where as thyroid weight increased significantly in mice treated with mancozeb for 30 days. However, thymus weight increased significantly only in the mice treated with mancozeb for 10, 20 and 30 days. In mice treated with mancozeb for 20 days caused significant decrease in the level of protein and a significant increase in the level of total lipids in the testis. However, there was significant decrease in the level of glycogen in the kidney. In mice treated with mancozeb for 30 days caused significant decrease in the levels of protein and glycogen and significant increase in the level of total lipids in the testis and liver and a significant decrease in the protein, glycogen and total lipids in the kidney. These observed effects of mancozeb on testis and biochemical constituents may be due to hormonal imbalance in any of the stages in the hypothalamo-hypophysial-testicular axis.