Background and Aim: It has long been known that the spermatogenic tissue is very sensitive to temperatures higher than its physiologic temperature and causing cessation of activity and resulting in sterility. This study investigated the effect of a standardized 40% ellagic acid extract of pomegranate on the histopathology, diameter, and epithelial thickness of seminiferous tubules in albino rats exposed to heat. Materials and Methods: Twenty-five male albino Wistar rats were randomized at 7-8 months of age to five treatment groups. Group C was not treated; Group T0 was treated with 0.5% of Na carboxymethyl cellulose (CMC) 2 ml/day and exposed to heat. T1, T2, and T3 were treated with 75, 150, and 300 mg/kg/day of a standardized 40% ellagic acid extract of pomegranate (Punica granatum L.), respectively. The animals were orally administered Na CMC or pomegranate extract and were exposed to sunlight for 15 min at 40°C-42°C for 14 days. The animals were sacrificed on day 15 and the testes were removed for histological evaluation and measurement of seminiferous tubule diameter and epithelium thickness. Results: The diameter of seminiferous tubules from rats exposed to heat and treated with 300 mg/kg/day pomegranate extract was larger and the epithelia thicker than those in the other groups (p= <0.05). The protective effects of the standardized 40% ellagic acid extract may have been mediated by its antioxidant activity. Conclusion: Compared with controls, administration of 300 mg/kg/day of a standardized 40% ellagic acid extract of P. granatum L. for 14 days increased seminiferous tubule diameter and epithelium thickness in albino Wistar rats exposed to heat. Keywords: diameter, epithelium thickness, heat, pomegranate extract, seminiferous tubule.