Abstract: Effects of sub lethal doses of Bacillus thuringiensis galleriae (Bt)on the a ctivities of esterase in the gut,hemolymph,and whole body of Galleria mellonel la were studied.The results showed that specific activities of esterase in the gut and whole body of larvae treated with Bt decreased while no change was foun d in isozymic composition of esterase compared with the larvae in the non treat ed control.The activities and isozymic composition of esterase in the hemolymph of G.mellonella larvae remained unchanged.