This project was carried out to study the effect of five different doses of electron-beam irradiation, including: 0 as control, 1.5, 3.5, 5.5 and 7.5 kGy on peroxidase (POD), superoxide dismutase (SOD) and polyphenol oxidase (PPO) activities of brown button mushroom (Agaricus brunnescens). The experiment was conducted using an electron beam accelerator (ESS-010-03) and measurements were made during 1, 4th, 8th, 12th and 16th day storage at 4 °C and 80 percent relative humidity. There was a significant difference between irradiated and non-irradiated (control) mushrooms in different enzymes (P<0.01). Most Peroxidase activity was observed in mushrooms treated with 7.5 kGy. The irradiated mushroom with 7.5 kGy also showed the highest SOD activity. The lowest SOD activity in mushrooms was related to control in all days of storage. The mushrooms irradiated with 0 and 7.5 kGy contained higher and lower PPO activity using pyrocatechol as substrate respectively, during 12th and 16th day compared with other doses. Treatment of 0 kGy induced the highest PPO activity using pyrogallol as substrate in storage days. The data increased the current understanding of the effects of electron-beam irradiation on the enzyme activity changes associated with postharvest senescence and should lead to more targeted strategies for reducing postharvest quality loss in A. brunnescens.