Spodoptera littoralis (Boisd.) is a major plant pest that causes substantial economic losses worldwide especially in vegetable crops. Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are generally considered beneficial organisms which can serve within integrated pest management (IPM) in agroecosystem. The effect of EPNs Steinernema sp. (EBN1e), and Heterorhabdities bacteriophora (EBN10k) that exposed to 11 different chemical pesticides on the cotton leafworm larvae was determined under laboratory condition. Generally, Steinernema sp. (EBN1e strain) exposed to different tested chemical pesticides was more affected on fifth instar larvae of S. littoralis than H. bacteriophora (EBN10k strain). More than 90% of fifth instar larvae of S. littoralis was killed after exposure to EBN1e strain treated with all used chemical pesticides except EPN1e strain treated with chlorfluazuron, thiocyclam and benomyl which caused 75.45, 80.65 and 81.5 % mortality of cotton leafworm fifth larvae respectively. In otherness, the mortality of fifth instar larvae of S. littoralis required to Heterorahbdities strain was less than Steinernema strain treated with different tested chemicals insecticides. There were significant differences in mortality of S. littoralis fifth instar larvae between EBN1e and EBN10k nematodes strains exposed to different chemical insecticides. The EBN1e strain was highly virulent than EBN10k in all treatments. In general, there was significant difference in mortality rates of cotton leafworm larvae required to EPNs concentrations (500IJs and 1000IJs) exposed to different chemicals and between exposure times.