Abstract: Based on the sequence of ClassⅣ chitinase gene which has been cloned by our research group from Chinese cabbage, a pair of specific primers were designed and the chitinase mature peptide gene CHB4 was amplified by RT-PCR. And then the prokaryotic expression vector pET-CHB4 was constructed, which expressed a protein of about 28 kD in Escherichia coli BL21 cells induced by IPTG. The expression protein was mostly composed of inclusion body and the solubility of expression products was not change in 25 ℃, on the other hand, There were recombinant protein bands in lysis supernatant while pH 9.5. At the 0.6 mmol/L IPTG, the restraining bacterium effect was remarkable and the chitinase activity reached maximum 2.8U.