Quantitative microscopic structure of testis in adult Arabian rams, raised under closed grazing system in Khuzestan province of Iran, was studied in four seasons over a one year period. For this purpose, thirty adult rams were randomly selected and the live weight and scrotal circumference of rams were recorded. At the beginning of each season, among the study group, four rams were randomly selected, slaughtered and their left testes were removed and weighed. For microscopic studies, tissue samples were excised from the left testes, fixed in Bouin’s solution and embedded in paraffin. Cross-sections (5 μm thickness) were stained with haematoxylin-eosin and evaluated with quantitative techniques. The results showed that scrotal circumferences, weight and volume of testis varied significantly throughout the year, with the lowest values in early summer (P<0.05). Seminiferous tubule diameter was highest in early winter (220.97 ± 12.15 μm). Also, relative and total volumes of seminiferous tubules and germinal epithelium gradually increased during the summer and autumn, with highest values in early winter. Higher relative volume of seminiferuos tubuli lumina (P<0.05) was found in early summer (%12.15 ± 0.35). Lower relative volume of interstitial tissue (P<0.05) was found in early winter (%15.70 ± 0.49). Scrotal circumference was significantly correlated with the seminiferous tubule diameter and the total volume of seminiferous tubules (r = 0.70, P<0.01). The results indicated that the stereological structure of testis in Arabian rams raised under closed grazing system in the Khuzestan province of Iran is highly affected by season.