Quantitative and qualitative analysis of the testis after zeranol implantation resulted in a change in the rate of frequency of the stages 7,8 and 1 of the seminiferous epi thelial cycle. Also the ratio of germ cells/Sertoll cells ( Sertoll cell ratio ) was relatively lower as well as the neutral lipids appeared in the form of larger droplets in the Sertoli cells in comparison with that of the control testis. Moreover, the number, size and shape of the interstitial cells were greatly affected and exhibited signs of decreased cellular activity in the implanted tested testis. It is conduluded that, zeranol Implantation significantly increased body weight and improve gain. Although it did not affect the synchronized initiation of successive cycles of the seminiferous epithelium it delayed the release and decreased the number of the spermatozoa.