The study was conducted to investigate the effect of oxidative stress induced by hydrogen-peroxide (1% in drinking water) and vitaminC (500mg/kg) on physiological characters of reproductive system in male rats, and the role of vitaminC in improving these changes. Administration of H2O2 for 30days resulted in significantly decrease in body and testis weight, head, body and tail of epididymis, seminal-vesicles and prostate. Decrease in ratio of live sperms associated with an increase in ratio of abnormal and dead sperm. Administration of vitaminC for15 days after fifteen days from exposure to 30days oxidative stress resulted in a clear improvement in body weights and weights of testes, head, body and tail of epididymis and prostate gland and seminal vesicles. The ratio of sperm abnormalities returned to the normal state. The percentage of dead sperms decreased and the percentage of live sperms increased significantly but didn't return to normal state. Treatment of animals exposed to H2O2 with vitaminC for 30days protected the animals from oxidative-stress as reflected by improvement in body and testes weight and others reproductive organs, percentage of live, dead and abnormal sperms, and diameter of seminiferous tubules. It is concluded that reactive oxygen-species produced by H2O2 are responsible for pathophysiological changes of male reproductive system and vitaminC has protective effect on hydrogen-peroxide-induced defect in the histophysiological aspects of this systems