Abstract: The protective effects of Mentha piperita leaf extract against radiation-induced damage in testis of Swiss albino mice have been studied. Animals (Male Swiss albino mice) were given M. piperita leaf extract orally (1 g/kg body weight/day) for three consecutive days before radiation exposure (8 Gy γ-radiation). Mice were autopsied at 1, 3, 7, 14, and 30 days after irradiation to evaluate the radiomodulatory effect in terms of histological alterations, lipid peroxidation, and acid and alkaline phosphatases levels in testis. Radiation treatment showed reduction in the testis weight during all days of observation, however, in the M. piperita leaf extract-pretreated irradiated group there was a significant increase in testis weight. Radiation treatment induced moderate to severe testicular atrophy with degeneration of germ cells in seminiferous tubules. The tubules were shrunken and greatly depleted of germ cells. Sertoli cells with few germ cells were observed in the lumen. However, animals pre-treated with M. piperita leaf extract and exposed to radiation showed normal testicular morphology with regular arrangement of germ cells and slight degeneration of seminiferous epithelium. Significant decreases in the lipid peroxidation and acid phosphatase level and increase in level of alkaline phosphatase were observed in testis. The M. piperita leaf extract showed high amount of phenolic content, flavonoids content and flavonols. The results of the present study suggest that M. piperita has a significant radioprotective effect and the amount of phenolic compounds, the content of flavonoids and flavonols of M. piperita leaf extract may be held responsible for radioprotective effect due to their antioxidant and radical scavenging activity.