A recombinant strain of Escherichia coli harboring a plasmid containing the Bacillus thuringiensis δ-endotoxin synthesis gene, was tested for its efficacy to synthesize δ-endotoxin, in a complex medium containing sucrose and yeast extract. Also, the recombinant E. coli strain was tested for its efficacy against the 2^nd instars of Spodoptera littoralis. The recombinant strain of E. coli showed a good activity against the 2^nd instars of S. littoralis, the mortality was 70 % after 7 days at room temperature. A high cell biomass (8.8gL^-1) and δ-endotoxin concentration (6.8 mg L^-1), were obtained by the shake flask culture (100 ml medium/250 ml flask, at 200 rpm), of the recombinant E. coli in modified MR medium containing sucrose (20g/L), as carbon source and yeast extract as nitrogen source, in the presence of CaCO₃, K₂HPO₄, MgSO₄, FeSO₄ and ZnSO₄ as mineral salts. The best pH values for cell biomass production and endotoxin production were 7.0 and 7.5, respectively. The corresponding figures for the best temperature were 37^oC and 30^oC, respectively. The use of some byproducts such as black-strap molasses, corn-steep liquor and cheese whey, as an alternative for carbon and nitrogen sources of medium, were found to enhance the cell growth but showed no effect on endotoxin production.