After the determination of insecticidal activity,one Bacillus thuringiensis strain,showing high toxic to Pieris rapae,Plutclla xylostella and Chilo suppressalis,was obtained and named Bt X-2.Degenerate primers were designed based on the N-terminal partial sequence of Cry1 to amplify the corresponding DNA sequence by touchdown PCR.The amplified fragment,with the length of 3 468 bp,encoding(1 155) amino acid with M_r=130 780 and pI=5.06.The amino acid sequence of Cry1Ab X-2 gene showed more than 95% identity to other Cry1Ab,and it was registered in GenBank(Accession No.AY847289).