The increased awareness of environmental pollution have led to the growing interests of the application of biological agents to control insects such as  lepidopteran family .Thus , this study aimed to produce genetically improved bioinsecticide agents to be  used  to control  Spodoptera litura  which would be useful in reducing environmental pollution ,preventing resistance to bioinsecticides and for safe food production .Four Bacillus thuringensis  strains were used as recipients ' while ' Seratia marcescens  was used as a doner strain in the conjugation to induce new recombinants in Bacillus thuringiensis over expressed chitinase.Four matings were conducted in this study between Serratia marcescence and  the four Bacillus thuringiensis strains which having opposite genetic markers.Two efficient transconjugants based on chitin hydrolysis on agar medium  were selected from each conjugation to be evaluated for  toxicites  against the larvae of cotton leafworm in relation to their parents .The efficient LC₅₀ was appeared by Tr₄ ( 1.93 x10⁵ ppm ) followed by Tr₆ and Tr₇ ( 2x10⁵ ppm). However , more than 995% toxicity index was recorded by Tr₄,Tr₆ and Tr₇. Higher toxicity index observed by these transconjugants may  be the related to the overexpression of chitinase genes.Therefore , the lethal concentration values obtained was  necessary to kill 50% of larval population from Spodoptera litura in a certain period .The virulence of Bt strains showed that a lower concentration from Tr₄ was required to kill 100% of larval population .It must be pointed out that higher toxicity index obtained by transconjugants reflected the interaction between crystal genes from Bt and chitinase genes from Seratia marcescens which enhanced the possibility of larval mortality as a genetic helpful tool in integrated pest management in cotton fields.