To prevent appearance of resistant mosquitoes against $delta$-endotoxin of bacillus thuringiensis subsp. israelensis (Bti) in field, a mosquitocidal Bacillus thuringiensis strain 21-2(Bt21-2) producing a new type of $delta$-endotoxin was isolated. The strain Bt 21-2 belongs to H serotype 43, B. thuringiensis subsp. guiyangiensis (Btg). The $delta$-endotoxins from the strain Bt 21-2 and the strain Bti were a cuboid shape morphologically, but the $delta$-endotoxin of the strain Bt 21-2 was composed of 150, 90 and 70kDa proteins on SDS-PAGE, and the antigenicity of $delta$-endotoxin of the strain Bt 21-2 was different from that of the strain Bti on immunoblot. The $delta$-endotoxin gene of the strain Bt 21-2 was not amplified with specific primers of $delta$-endotoxin gene (cry4A and cry4B) of the strain Bti on PCR.