Abstract: The aim of this research was to evaluate the effect of deprenyl (selegiline), a monoamine oxidase-B inhibitor (MAO-B) on pituitary-gonad axis and spermatogenesis in rats. In this study 32 adult male rats in the form of experimental and control groups were used. The experimental groups (B, C and D) were given oral doses 5, 10 and 15 (mg kg-1 B.W) selegiline for the period of 30 days and the control group (A) received normal saline. The blood samples were taken 8 h after receiving last dose on 30th day and the concentrations of Lutein Hormone (LH), Follico Stimulating Hormone (FSH) and testosterone were measured by RIA. In addition, on the 30th day the testes were separated and histological changes were studied among experimental and control groups. The difference in concentration of hormones between groups were studied by one-way analysis of variance (ANOVA), followed by Tukey test. The level of significance was considered at p≤0.05. The results indicates that receiving different dosage of selegiline shows a significant increase in concentration of LH hormone in comparison with control group, but concentration of FSH did not show significant difference in comparison with the control group. In addition the concentration of testosterone in response to different dosage in relative to the control group shows a significant decrease. According to the results we suggest that selegiline causes a decrease in concentration of testosterone via down-regulation receptors on leydig cells by LH. Furthermore, as an inhibitor of MAO-B, causes increase in dopamine concentration in striatum area and in turn causes decrease in concentration of prolactin. The decrease of prolactin secretion reduce the effect of LH hormone on leydig cell. Besides, histological studies showed a significant effect caused by selegiline such as decrease of sperm in seminiferous tubules, leydig cells and reduced spermatogenesis.