Endosulfan is an organochlorine pesticide that is widely used throughout the world for higher agricultural production. Its extreme toxicity, however, has caused health and environment concerns that have led to an interest in detoxification. In this study, the radiolytic degradation of endosulfan was investigated. Endosulfan in methanol solution (100 ppm) was irradiated at 0, 10, 30, and 50 kGy, and subsequent changes in immune toxicity and degradation of endosulfan were observed. The concentration of endosulfan that was used in this experiment did not affect the cell proliferation. The irradiation of endosulfan decreased the production of NO, indicating a decrease in the immune toxicity of endosulfan by irradiation. The concentration of endosulfan was significantly reduced by irradiation in a dose-dependent manner. The results suggest that gamma irradiation can degrade endosulfan and can reduce its immune toxicity.