Abstract:Three strains of Bacillus thuringiensis were isolated from the larvae of Dendrolimus sibiricus, Pyralis farinalis and from forest soil. The parasporal crystals of the strains were examined by electronic microscopy, wich showed three kinds of form: the bipyramidal and mosaic the cuboidal and the irregular. The biochemical characters of the three strains and esterase analysis of vegetative cell were examined. The three strains showed different toxicity to the test insects.