Two species of the Entomopathogenic nematodes, Steinernema carpocapsae and Steinernema scapterisici were studied against cotton leaf worm Spodoptera littoralis (Boisd) and black cutworm Agrotis ipsilon (Hufn.).Under laboratory conditions, by using different nematodes strains at Lc₅₀ values were 3, 6, 7 juveniles IJ/ml of S. scapterisici , S.carpocapsae , combination of both strains and using water for control .The results investigated that effect of all treatments on some biological aspects of target pests such as, larval duration of  S. littoralis were  recorded that, 11.5, 11.5,11 and 11.8 days, after treatments with S.carpocapsae , S. scapterisici, combination and control, respectively. Furthermore A.ipsilon showed that highly tolerance more than cotton leaf worm,also the percentages of larval mortality were 32 % for S.carpocapsae ,44 %  for S. scapterisici, 26% for combination of both strains and no larvae mortality on control treatments. Also there is no significant differences between pupal duration of both target pests while, the results indicated that, significant differences between pupal weight (mg) of S. littoralis and A. ipsilon. No emergency of S.littoralis moths after treatment with strain S.carpocapsae and this percentage increased to 66 % with S. scapterisici, however the combination of both strains affected the emergency of moths to reach 33% compared with control 84%. As regard the 2^nd insect pest A.ipsilon showed that highly emergency of moths 92 % for control treatment with water only and 50 % when treated with S. scapterisici and combination of both strains while decreased to 33% for  S.carpocapsae. Subsequently, all the biological aspects of adults of both pests as ovi-position, fecundity (Eggs/ female), fertility and also the intermediated shapes were affected mostly by S. scapterisici, these findings might be taken into consideration in evaluating the success of the Entomopathogenic nematodes as a pathogenic insecticides for S.littoralis and A. ipsilon as an economic pests of cotton plants and opens new approaches to develop highly efficient combined biological products on the basis of entomopathogenic nematodes as a bio-agents.