Abstract: To determine the minimal active fragment of Cry1Ba3 protein, six fragments of cry1Ba3 gene with different length were amplified using PCR with different specific primers. These fragments were cloned into pET-21b vector at BamHI and SalI restriction enzyme sites, and then introduced into E. coli BL21 strain. After induced with IPTG, the proteins expressed by different fragments were analyzed by SDS-PAGE, and the result showed that all these truncated proteins could be expressed in E. coli BL21. Bioassay result against Plutella xylotella showed that the minimal active fragment of Cry1Ba3 protein was located between amino acid No. 22 and No. 655. Because the insecticidal activity of the truncated protein containing amino acid No. 54-655 was declined significantly, and No. 22-627, No. 85-655 was lost completely, while the toxicity of fragment including amino acid of No. 22-655 was not changed with original Cry1Ba3

Key words: Bacillus thuringiensis, Cry1Ba3, active domain, Plutella xylotella