A strain of Bacillus thuringiensis, STB-1, toxic against Spodoptera exigua, was isolated. Bacillus thuringiensis STB-1 produced bipyramidal inclusions and reacted with the H antiserum of B. thuringiensis ssp. kurstaki. The plasmid and protein profiles of B. thuringiensis STB-1 were compared with those of its reference strains, ssp. kurstaki and ssp. kenyae. To verify the gene type of B. thuringiensis STB-1, PCR analysis was performed with Spodoptera-specific cry gene primers. The result showed that B. thuringiensis STB-1, unlike its reference strains, had crylAa, crylAb, crylAc and crylE, suggesting that B. thuringiensis STB-1 was a unique strain with respect to gene type. In addition, B. thuringiensis STB-1 showed a high level of toxicity against both S. exigua and Bombyx mori, whereas B. thuringiensis ssp. kurstaki HD-1 or ssp. kenyae showed a high level of toxicity against only Bombyx mori or S. exigua, respectively.