Although the association between 5-alpha reductase inhibitors and infertility is well established, the impact of these agents on testicular histology is not clear. The aim of this study is to evaluate the alterations in the histological structure of testes in rats treated with daily dutasteride. A total of 18 male Sprague-Dawley rats (5.5- 6 months old) have been divided into 2 groups. Group-C (n=8) served as the control group and Group-D (n=10) received dutasteride 0.5 mg/rat/day p.o. Rats were sacrificed and their testes were harvested for histopathological and biochemical evaluation at the 30th day. Johnsen’s criteria (a score of 1 to 10 for each tubule cross-section by staining with H&E, 400x as shown figure 1) were used to assess spermatogenesis. Serum hormone levels were measured by ECLIA whereas levels of reactive oxygen species (ROS) in both testicular tissue and serum were evaluated by ELISA. Results were compared with Mann- Whitney U test and statistical significance level was set as p<0.05.