The potency of three commercial bio-insecticides, Protecto namely, Bacillus thuringiensis var. kurstaki, Viruset, Spodoptera littoralis Nuclear Polyhydrosis Virus, SLNPV and their mixture Profect were evaluated against the cotton leaf-worm, Spodoptera littoralis(Boisd.) (Lepidoptera: Noctuidae). Protecto proved to be more toxic on both 2nd instar larvae than the two other tested bioagents, Viruset was more effective on 4th instar larvae than Profect. LC90 and LC50 for Viruset were 1x106 and 1x103 PIBs/ml, respectively, corresponding values were 5x108+1.6x107 and 5x104 + 1.6x103 PIBs/ml + IU/ml when Profect was tested. The tested bioagents reduced larval duration, percentages of larval pupation as well as adult emergence of S. littoralis fed as 2nd instar larvae on castor oil leaves treated with LC50 .The digestive enzymes amylase and invertase and trehalase were determined in 6th instar larvae surviving treatment of 2nd instar larvae with LC50 of the tested three bioagents. Amylase activity in treated larvae was found to be significantly higher in all treatments . Similarly, except in case of Viruset, invertase activity was increased. Meanwhile, the three tested compounds caused a significant decrease in trehalase activity.Midgut histological sections were carried out on 6th instar larvae treated as 4th instar larvae with LC50 of the three tested compounds. Profect was the most effective product in causing aberrations in the midgut layers, following by Protecto and Viruset.