A Bacillus thuringiensis designated NT0423, belonging to B. thuringiensis subsp. aizawai (H 7), was isolated from samples of dust and soil of sericultural farms. B. thuringiensis NT0423 having dualspecificity against Lepidoptera and Diptera produced bipyramidal inclusions consisting of two major polypeptides of approximately 130- and 70-kDa. Proteolytic processing by trypsin and gut juice of Bombyx mori yielded predominant proteins with molecular masses of about 66-kDa. The whole crystal protein of B. thuringiensis NT0423 immunologically was related to that of B. thuringiensis subsp. aizawai. PCR analysis showed that B. thuringiensis NT0423 has at least five crystal protein genes including cryIA(a), cryIA(b), cryIC, cryID and cryIIA, and southern blot was determined the location of each gene on intact and enzyme-digested plasmid DNA fragments. Except for cryIA(a) gene on the high molecular weight plasmid of 165-kb, all of four genes were located on the plasmid of 66-kb. The production of $eta$-exotoxin from B. thuringiensis NT0423 was identified by the HPLC analysis. In addition, the $eta$-exotoxin showed its ability to prevent pupation of treated larvae of house flies (Musca domestica) from developing into normal adults.