Laboratory experiments were  conducted in 2008 at biological control department, plant protection research institute Sakha Kafr El-Sheikh station to study the efficacy of the fungus Beauveria bassiana (Bals.). An isolate collected from Sesamia cretica larvae in Kafr El-Sheikh region and cultured on potato dextrose agar medium (PDA) at 25 °C spore suspensions at concentrations of 1x10⁷, 2.5x10⁷, 5x10⁷, 7.5x10⁷ and 1x10⁸ spore/ml were prepared in distilled water containing 0.1% Tween 80. The larvae were individually treated by dipping method in the fungus suspension and bioassayed against the third larval instar of each species, Ostrinia nubilalis (Hbn.), Sesamia cretica (Led.) and Chilo agamemnon (Bles.) incubated at 25+1°C and 75+5 % RH). All tested concentrations induced different mortalities. For O. nubilalis L₃, mortality ranged between 5-100 % was reached at 4-10 days with the all tested concentrations LC₅₀ value was 1.2127x10⁷ after 12 days while LC₉₀ reached 9.7625x10⁷ spore/ml, respectively, meanwhile LT₅₀ values reached 12.7, 10.5, 8.6, 8.2 and 7.6 days with the tested concentrations of 1x10⁷, 2.5x10⁷, 5x10⁷, 7.5x10⁷ and 1x10⁸ spore/ml, respectively. As for S. cretica L₃, the highest mortality (75-90%) was achieved at 12-14 days post treatment. LC₅₀ value was 8.5037x10⁷ while LC₉₀ was 15.05x10⁷ spore/ml at the same mentioned period meanwhile, LT₅₀ values reached 17.4, 14.8, 11.0, 10.7 and 8.5 days by all tested concentrations. In case of C. agamemnon L₃ the highest mortality reached 80-90 % after 12-14 days of treatment. LC₅₀ value was 1.5884x10⁷, while LC₉₀ was 9.8329x10⁷ spore/ml., at 14 days post treatment, LT₅₀ values were 15.5, 11.8, 8.8, 8.6 and 8.1 days for the concentrations of 1x10⁷, 2.5x10⁷, 5x10⁷, 7.5x10⁷ and 1x10⁸ spore/ml, respectively.