According to the amino acid sequence of CM4 and the bias for preferred condons of E. coli, the CM4-like gene was obtained by a recursive PCR (rPCR) strategy using two lapping oligonucleotides. The synthesized gene was coloned into the expression vector pET32(a) and transformed into E. coli BL21 (DE3). Recombinant CM4-like gene expression was driven by the T7 promoter on the vector upon addition of IPTG and high level of expression was achieved. The solube protein was purified by Ni-chelating agarose and treated with formic acid. After cleavege, the recombinant peptide was purified by another Ni(2+)-NTA-Agarose affinity chromatography and cation-exchange chromatography. Results of agarose diffuse assay and liquid turbidity analysis indicated that the recombinant peptide exhibited the antibacterial activity.