Background: Vitamin D is an essential vitamin of body that helps to grow and strengthen the bones. In the present study, the Protective effect of vitamin D on function and testicular tissue in adult rat treated with thioacetamide was studied. Materials and methods: In this experimental study, 48 adult male Wistar rat weighing 180-200 g were divided into 6 groups of 8. Control group did not receive any solvent or extract. Sham group received daily 1ml of distilled water as solvent for 25 days by gavage method. Experimental group1(negative sham); once daily, 1000 IU/kg of vitamin D was taken as gavage for 25 days. Experimental group1(positive sham); once daily, 50 mg/kg of thioacetamide was taken as gavage for 25 days. Experimental group 3 and 4 received doses of 500 and 1000 IU/kg of vitamin D with 50 mg/kg of thioacetamide by gavage method, respectively. On the 25th day, the final weighing was done and after anesthesia, the rats received direct blood sampling from the heart to measure the hormone levels of LH, FSH and testosterone. The testicles were removed and after weighing and preparing microscopic sections, staining with hematoxylin-eosin and at the end of the histological examination of the testicle. Data were analyzed based SPSS program and ANOVA. Results: The results showed that the mean right and left testicle weight and number of sertoli cells in all experimental groups did not change significantly compared to the control group.The mean body weight in all experimental groups was significantly lower that the control group. The mean serum concentration of testosterone , FSH hormones , number of primary spermatocyte and spermatid cells in experimental groups 2 and 3 were significantly lower than the control group. The mean serum concentration of LH hormone and number of leydig cells in experimental groups 2, 3 and 4 was significantly lower than the control group.The mean number of spermatogonia cells in the experimental group 2 showed a significant decrease compared to the control group (P
