The present study was conducted Aga district El-Dakhlia governorate, throughout 2006 and 2007cotton seasons. During the course of this study, three strains (I, II and III strains) of entomopathogenic bacteria belonging to Bacillus thurengeinsis Berl. were isolated from the pink (PBW), Pectinophora. gossypiella (Saund.), spiny (SBW), Earias. insulana (Boisd.) and American (ABW), Helicoverpa. armigera (Hub.) bollworms. In addition, two bacterial pathogens namely, (Streptomyces avermecti and Micrococcus sp.) were isolated from the previously bollworm larvae. The pathogenicity of each pathogen suspension was evaluated under laboratory conditions against the fourth larval instars of ABW, SBW and PBW. Statistical analysis indicated that B. thurigiensis strains (especially strain I) induced the highest pathogenicity to ABW, SBW and PBW larvae, while S. avermecti ranked second in the order of activity. Micrococcus sp. induced the lowest pathogenicity. The efficiency of the local strain (I) of B. thurigiensis in comparison with the commercial isolate (Agerin)was evaluated under field conditions. The In the first season (2006), the mean reduction percentages of infestation caused by PBW, SBW and ABW were 61.8, 65.5 and 74.2% in cotton fields treated with the local isolate (B. thurengeinsis strain I), while,the mean reduction percentages of infestation in Agerin treatment were 48. 5, 56.9 and 66.1%, respectively in comparison with control. In the second season (2007), the mean reduction percentages of infestation were 60.4, 55.6 & 63.5% for local isolate of B. thurigiensis and 47.7, 46.0 & 52.4 % for Agerin treatment, respectively.