The insecticidal crystal protein(s) encoded by cry gene(s) of Bacillus thuringiensis (Bt) have been used for insect control both as biopesticides and in transgenic plants. A new 3'-truncated cry1Ab gene was cloned from an indigenous isolate of Bt, A19-31. Nucleotide sequencing and homology search revealed that the deduced amino acid sequence of Cry1Ab toxin of Bt strain A19-31 had a variation of two amino acid residues with the holotype sequence, Cry1Ab1. Expression of the 3'-truncated cry1Ab gene was studied in an acrystalliferous strain of Bt (4Q7). SDS-PAGE and immunostrip analysis of spore-crystal mixture revealed a low level expression of the 3'-truncated cry1Ab gene. Insecticidal activity assay showed that the recombinant 3'-truncated cry1Ab gene product was toxic to larvae of both Helicoverpa armigera and Spodoptera litura.