Laboratory tests and a semi-field trial were carried out to determine the efficiency of two commercial preparations of the entomopathogenic fungi,Beauveriabassiana and Metarhiziumanisopliae namely; Biosect w.p., and Bioranza10 % w.p., against the first instar larvae of the cotton leaf worm, Spodoptera littoralis(Boisd.) and, Agrotis ipsilon(Hfn.)(Lepedoptera : Noctuidae). Newly hatched, one- day and two- day old larvae of the two insects were allowed to feed on castor oil leaves (100 gram / replicate) treated with different concentrations of the two entomopathogenic fungi for 48hrs at three different temperatures, 20, 25 and 30⁵C. Mortality rate increased by increasing the concentration, or post treatment period and temperature. Newly hatched larvae were the most sensitive to the toxic effect especially at highest concentration and temperature(30⁵C), while the two- day old larvae were the most tolerant and the one-day old larvae expressed a moderate tolerance. S. littoralis was more sensitive than A. ipsilon. Calculated LC_50s values for initial mortality of the newly hatched larvae were (0.458, 0.309 and 0.279 mg/ml. when treated with Biosect and (0.676, 0.352 and 0.317 when treated with Bioranza) at 20, 25 and 25 ⁵C, respectively. Consumed castor oil leaves were decreased by increasing the concentration and temperature but were lower than the control.