Background: Onion has significant blood sugar lowering action. Objective: Antioxidants have essential effect on spermatogenesis and sperm parameters. Streptozotocin can dioceses oxidative stress and changes in antioxidant capacity are considered to play an important role in the pathogenesis of chronic diabetes mellitus. Methods: Wistar male rat (n=30) were allocated into three groups, control group (n=10) and oninon (O) group that received 1cc/rat (gavages) (n=10), and Diabetic group that received 55mg/kg (IP) streptozotocin (STZ) (n=20) which was subdivided to two groups of 10 STZ group and treatment group. Treatment group received 55mg/kg (IP) STZ plus15mg/kg (O), daily for,4 weeks, respectively however, the control group just received an equal volume of distilled water daily(gavages). Diabetes was induced by a single (IP) injection of streptozotocin (55mg/kg) .Animals were kept in standard condition. In 28day after inducing diabetic 5cc blood were collected for testestrone, TAC, MDA and Ox-LDL levels and testes tissues of Rat in whole groups were removed and sperm was collected from epididymis then prepared for analysis. Results: Sperm population, percentage of sperm viability and motility and Serum total testosterones significantly increased in group that has received 1cc/rat onion (p<0.05) in comparison to control and experimental groups. Testes weights in streptozotocin group significantly decreased in comparison to control group (p<0.05). Conclusion: Since in our study 1cc/rat onion have significantly Preventive effect on Sperm percentage of viability and motility and serum total testosterones by reducing level of Reactive Oxygen Species (ROS) in serum, so it seems that using it can be effective for sperm healthy parameters in Diabetic Rat.