In this study, the effects of gamma irradiation on the chemical constituents and antioxidant activities of peppermint essential oils and hydro alcoholic extract have been investigated. The results indicated that the major compounds of Mentha piperita were menthol, menthone, α-gurjunene, neo-menthol and 1,8-cineole. The oil main components were not considerable changed due to irradiation. Also, the total flavonoid content of the hydro alcoholic extract was unchanged after irradiation. In addition, the antioxidant activities of the oils and extracts stayed at a high level even after irradiation. Therefore, the application of the irradiation process can be suggested for the decontamination of peppermint without changes in the composition and antioxidant properties.