Secondary metabolites of entomopathogenic fungi have been known to suppress the immune response of various insects. Hence, we have investigated the effect of endophytic fungus, Alternaria alternata on cellular and humoral immune response of Spodoptera litura (Fabricius). Significant drop in total hemocyte count has been observed in the larvae fed on diet supplemented with ethyl acetate extract of A. alternata as compared to those fed on untreated or control diet devoid of ethyl acetate extract. Similarly differential hemocyte count of the larvae feeding on amended diet differed significantly from control. As compared to control significantly higher percentage of hemocytes exhibited abnormalities like aggregation, change in shape, extensive vacuolization and necrosis. The cytotoxic effect showed a dose dependent response which increased with time. A reduction in phenoloxidase and lysozyme activities was also observed. The data suggest that the secondary metabolites produced by A. alternata disabled several immunemechanisms of the insect. These studieswould help to identify the insect defenses that could be manipulated to accelerate host death due to fungal endophytes.