The antimicrobial peptide CM4 is a 35-residue cationic peptide. To explore a new approach for the expression and purification of CM4 in Escherichia coli, the CM4 gene was cloned into the vector pET32a to construct an expression vector pET32a-CM4. The fusion protein Trx-CM4, purified by Ni2+-chelating chromatography, was cleaved by hydroxylamine hydrochloride to release recombinant CM4. Purification of recombinant CM4 was achieved by reverse HPLC chromatography, and about 1.4 mg/l active recombinant CM4 with the purity more than 98% was obtained. The recombinant CM4 showed antimicrobial activities that were similar to synthetic one.