The aims of this study were to analyse the results of proximal edn ligation of male reproductive tract of Sprague-Dawley rats prior to maturation and to observe the different biological effects between experimental obstruction of the vas deferens before and after sexual maturation and of excretory function of vas deferens in the adults. After obstructing the vas deferens of Sprague-Dawley rats prior to sexual maturation, the morphological changes of testis and epididymis were observed and compared these changes with those occurring after blocking vas deferens in the adults, by observing the incidence and sites of spermatic granuloma. Bilateral vasectomy and sham operation were done on 10-day-old Sprague-Dawely rats. The operated Sprague-Dawley rats were separated into two groups in the postborn intervals of 24, 30, 40, 50, 80, 90, 100, 130 days. There were no significant differences of weight and volume of testis between vasectomized(Vx) and sham operation(SHAM) group even up to 130 postborn days. Although, some insignificant temporary changes were observed, there were no significant differences of testis histology between Vx and SHAM group. In a large portion of Vx group, sperm granulomas were observed mainly in the tail portion of epididymis after Sprague-Dawley rats matured. Due to this results, there were significant statistical differences of weight of epididymis between Vx group and SHAM control group after the Sprague-Dawley rats matured. When obstructed prior to sexual maturation, the testes were affected only transiently and showed no significant histologic changes comparing to the control group but significant epididymal alterations occurred: spermatic granulomas were observed much more common in epididymis than in vas deferens. With these results, it may be suggested that if we delay the vasovasostomy of obstructed or damaged vas deferens prior to sexual maturation until sexual maturation, the success rate will be significantly reduced due to linear growth of vas deferens and spermatic granuloma of epididymis. Therefore, clinically, it is most effective to perform vasovasostomy of obstructed or damaged vas deferens as soon as possible and if delayed, it seems to be wise to perform vasoepididymostomy after identifying the presence of epididymal granuloma.