Bio-agent compounds of Bacillus thuringiensis, Kurs. (Bactericide); Metarhizium anisopltiae, Metsch. (Fungicide) and biopolymer, chitosan exposed to gamma irradiation doses; 15, 30 and 60 Gy to purpose of potentiate the bio-agent efficiency against the cotton leaf worm, Spodoptera littoralis (Boisd.) treated as 4^th instars larvae by LC₅₀ of tested bio-agent compounds singly or combined with gamma irradiation doses to investigate the histopathological changes in the integument, muscle, fat body and mid gut. Most of treatments especially gamma doses of 60 Gy singly or combined with bio-agent compounds caused thickening of outer cuticle fibrous layer in the integument of S. littoralis larvae. Also, hypodermis layer had swelling and necrosis in gamma treatments and M. anisopltiae or chitosan combined with 30 Gy treatments. Also, most of treatments caused appearance of fissure and breaking down of muscles into small parts. All the bio-agent treatments caused a noticeable destruction on the fat body cells as vacuolization of the fat cells and destruction of the fat body membranous sheath. Many deleterious effects in the mid gut of S. littoralis as destruction of columnar or hyperphesia cells lining mid gut, losses of brush border with increase of goblet cells. Dose of 60 Gy is considered the best dose used in the current study to potentiate the bio-agent effects on S. littoralis larvae compared with other gamma irradiation doses used.