The effect of gamma irradiation on the different developmental stages of the Plodia interpunctella was studied. Eggs less than 24 hr. old, larvae 2 week-old and fully grown pupae were irradiated with 60, 80 and 100 Gy. Hatchability drastically decreased in the treatments compared with control, the incubation period slightly increased by increasing the radiation dose from 60 to 100 Gy. About seven percent of treated eggs were pupated but did not emerge to adult. While, increasing dose to 80 Gy caused death for all individuals. Larval and pupal duration prolonged by increasing the dosage. In general, irradiation reduced the life span of the resulting adults. Sex ratio seemed to be affected in favor of males at larvae. Fully grown pupae showed the same trend. However, sex ratio shifted in favor of females. Malformed adults increased by dose increasing. It might be summarized that the susceptibility of P. interpunctella was radiation-dose dependent.