Introduction: The present work aims to examine the possible role of stem cells on biochemical markers and histopathological alterations of hypoxia caused by sodium nitrite (NaNO 2 ) toxicity in testes of male rats. Methods: In this study, 96 adult male albino rats were divided into 6 groups (16 rats each). Group 1 (G1) was the control group and received distilled H 2 O. Group 2 (G2) received daily NaNO 2 (35 m/kg bwt/ day) via subcutaneous injection for 3 weeks. Group 3 (G3) received NaNO 2 for 2 weeks and were then injected once with 2*10 6 mesenchymal stem cells (MSCs) intravenously and sacrificed 4 weeks later. Group 4 (G4) received NaNO 2 for 2 weeks and were then injected with 2*10 6 MSCs followed by daily NaNO 2 injection for 1 week; rats in G4 were sacrificed 4 weeks from MSCs treatment. Group 5 (G5) rats were treated with NaNO 2 for 2 weeks and then left to recover for 4 weeks. Finally, Group 6 (G6) rats were treated with NaNO 2 for 3 weeks and left to recover for 3 weeks, after which point they were sacrificed. Results: The results showed that NaNO 2 caused oxidative damage and histopathological alterations in the rat testes, as well as increased the levels of testes malondialdehyde (MDA), nitric oxide (NO) and DNA fragmentation percentage (DNA F %). Moreover, NaNO 2 decreased the elevated activities of testes catalase (CAT) and total antioxidant activity (TAA), in comparison to the control group. The histological results illustrated different distortions, vacuolization and lipid accumulations in interlobular space as well as diminution of inter cellular germ cell layers, absence of Leydig cells, irregular basement membrane of tubule, and separation within spermatogenic cells. In