In the present work, two cultures of Bacillus strains belonging to two serotypes and four of their transconjugants were screened with respect to their activities against lepidopterous cotton pest. Two strains of Bacillus were screened for their drug resistance to be used as a genetic markers to identify bacterial strains in the conjugation process. B. subtilis was found to be sensitive to all antibiotics and drugs, and also resistant to crystal violet. Although, B. thuringiensis was found to be sensitive to all antibiotics, drugs and crystal violt, except for it was resistant to hiconcil. Bacterial transconjugants isolated from conjugation between both strains were more resistant to both crystal violet and hiconcil. Two groups of crystals and spores have been isolated within Bacillus strains and their transconjugants. This because -endotoxin gene of B. thuringiensis codes for the insecticidal crystal protein (ICP) specific for lepidopteran insects, since the N-terminal half of the toxin is sufficient both for insect specificity and toxicity. The potency of two Bacillus preparation was determined against Spodoptera littoralis. The toxicities of these two groups against larvae of Spodoptera littoralis expressed as; average consumption of fed leaves, average weight of surviving larvae, survival percent of the larvae and mortality percentage are also differed. Mortality levels of larvae caused by the different isolates varied from 20.83 to 79.17 (crystals alone) and from 58.33 to 83.33 (crystal and spores). Higher levels of mortality were observed if a mixture of relatively pure crystals and spores was used compared with the mortality resulting from either fraction of crystal alone. -endotoxin recombinant crystalline protein and endospores from bacterial transconjugants were highly toxic effective against S. littoralis than from their parental strains.