The aim of the present study is to improve the insecticidal activity of the entomopathogenic Beauveria bassiana by adding Chitosan to its secondary metabolites. The secondary metabolites were extracted from the broth culture of B. bassiana by ethyl acetate solvent. Chitosan was extracted from shrimp shells via three steps; demineralization; deproteinization and de acetylation. The joint action between secondary metabolites and chitosan was determined by calculating the synergistic ratio and co-toxicity coefficient against the cotton leaf worm Spodoptera littoralis as an economic insect pest. Also, the effect of both compounds and their mixture on the larval growth and feeding were studied. The results indicated that the mixture of both compounds was more toxic than the individual compound. Likewise, the toxicity of secondary metabolites was the highest compared with chitosan effect. The obtained results from synergistic ratio and co-toxicity coefficient formula revealed to presence the synergism and potentiation between secondary metabolites and chitosan. In addition, larval growth and consumed diet were decreased in case of the mixture of secondary metabolites and chitosan more than individual case. Finally, this study recommended that using chitosan as an additive substance increase the efficiency of secondary metabolites of B. bassiana against the cotton leafworm S. littoralis. Also, the mixture of both extracts considered an effective insecticide and safe for the environment.