In this investigation Three different methods for isolation of crystal toxin from B. thuringiensis kenyae and kurstaki were evaluated. Results indicated that PEG-sodium dextran sulfate capable of separating more than 21% of crystalline toxin produced by strain kenyae from spore / crystal mixture with purity of 99%. According to this study, isopycnic zonal centrifugation utilizing sodium bromide gradient was found to be convenient for isolation crystals from strain kurstaki which produced 25 % crystal toxin from spore — crystal mixture.. Spontaneous mutants for ampicillin and streptomycin resistance was obtained as a genetic marker for identification of fusant cells., also spontaneous a rystalloferous mutants from both strains were obtained for demonstrating plasmid profile and their relation to crystal — toxin production. Results indicated that 135 MDa. plasmid transferred to a crystalloferous cells converting them to a cryatal forming one. In this work, optimized conditions for protoplast formation, regeneration, and fusion were obtained. Results indicated that 6 mg / ml lysozyme treatment for 24 - 30 min convenient for obtaining high frequency protoplast formation and regeneration. Regeneration was found to be enhanced through the addition of 20 % gelatin to the regeneration medium. Factors affectin protoplast fusion were taken hi account such as PEG concentration temperature, and time course of treatment It was found that using PEG concentration of 40 % atincubation temperature 28 °C for two min was optimum to obtain high fusion frequency. Results obtained from improvement of B. thuringiensis strains by protoplast fusion indicated that there is • an increasing in potency when fusant cells were tested against Ephestia caledilla. Fusant cells showed an increase in biomass production, where as rescipient cells showed an increase in toxin production to about 13.5 %. Conjugation like process was used in this work as a tool lor improving B. thuringiensis strains.