the objective of this study was to show the susceptibility of different immature stages (eggs, larvae and pupae) of potato tuber moth Phthorimaea operculella (Zeller) (Lepidoptera: Glechiidae) to the entomopathogenic fungus (EPF) Beauveria bassiana, and the effect of irradiating full-grown male pupae of ph. operculella at sub-sterilizing doses 100 and 200 Gy of gamma irradiation (alone and in combination with LC50 of B. bassiana) on some biological aspects of resulting F1 larvae, the results showed that, the EPF B. bassiana was pathogenic to all immature stages with LC50 values of 5.5x103, 28.56 and 1.1x105 conidia/ml, respectively, larvae were more susceptible to infection by B. bassiana than eggs and pupae. The percents of larval and pupal mortality were increased as the radiation doses increased while the percents of pupation and adult emergence were decreased as the radiation dose increased. Combination of gamma radiation and B. bassiana was more effective than either treatment of them alone.