The reproductive activity is influenced by environmental conditions in most animal species. The aim of the present study was to determine the seasonal changes of seminiferous tubules structure and spermatogenic activity in Khouzestan Arabian rams. For this propose 30 adult rams were reared under closed grazing conditions. Four rams were randomly selected in each season and their live weight, testicular weight and diameters were measured and recorded. Furthermore, their blood sera were collected for measuring testosterone by radioimmunoassay. For microscopic studies, the 5-6fl sections were made and stained with Haematoxylin-Eosin. Results showed that testicular weight and diameter were significantly changed by season (p<0.05) and the minimum values were seen in the beginning of summer. While spermatognic activity was present in all seasons, structural changes were seen in seminiferous epithelium. The seminiferous tubule diameter and germinal epithelium height showed a gradual increase during different seasons during summer and autumn and the maximum values were seen in the beginning of winter. The maximum plasma testosterone was seen in the beginning of winter and significant decrease shown during spring (p<0.05). Seminiferous tubule diameter showed significant correlation with testicular diameter and testosterone levels. It can be concluded that spermatogenic activity of seminiferous tubules in adult khouzestan Arabian rams are highly affected by season.