The seed bug Graptostethus servus (Fabricius) (Hemiptera: Lygaeidae) is a pest, recently recorded in Egyptian oil crops, such as sesame (Sesamum indicum), sorghum (Sorghum bicolor), cotton (Gossypium hirsutum) and sunflower (Helianthus annuus). This work is considering the impact of the native isolate of the entomopathogenic fungus Beauveria bassiana (Ascomycota: Hypocreales) against G. servus. The results revealed that G. servus is very vulnerable to B. bassiana. LC₅₀ value was 2.9x10⁶ spores/ml and the LT₅₀ value was 4.16 days. The infection affected various body parts, especially the cuticle and the midgut. The application of B. bassiana on the adultʼs cuticle resulted in an apparent disturbance in the structure of the cuticle and degeneration of its different parts. These changes were observed 48 hours after treatment and increased in severity over time. The fungal infection was not limited to the cuticle, but also affected the epithelial cells of the crop and midgut, as well as the mesenteric caeca. These results highlight the insecticidal potential of the fungus B. bassiana against the pest G. servus.