Cypermetherin has been implicated in the development of a variety of reproductive disorders in humans and infertility in wild life, where it increases the death rate of the offspring and induces aggressiveness (Elbetieha et al., 2001). Studies in workers exposed to handling of agro pesticides indicate that they have defects in their reproduction capabilities characterized by infertility and/or a decrease in the fertilizing potential, fetal death. In this study, mice weighing 30-35 g were used, separated in 3 groups, (1) control (2) vehicle (oil) and (3) experimental (Cypermetherin and oil). The animals were gavaged by 1/5, 1/20 LD50 for 2 and 4 weeks respectively, and with 1/5 LD50 for 12 weeks, then sacrificed. Epididymal spermatozoa were evaluated with respect to quantity, motility and morphology. The histology of testis and epididymis was also studied. Sperm count decreased by around 20% in treated animals compared with control. Teratology observations showed a clear modification of sperm morphology, especially the flagella. Testicular and epididymal morphology was also impaired. It is concluded that Cypermetherin may cause morphological and functional alteration of the male reproductive tract.