LEAP2(Liver expressed antimicrobial peptide-2) antibacterial peptide is a kind of small molecular peptide expressed mainly in the liver of animals, and they play important roles in the immune systems of animals. The primary structure of LEAP2 from channel catfish(Ictalurus punctatus) is composed of signal peptide and prepeptide which is composed of 66 amino acid residues. The 41 residues near carboxyl terminal of the prepeptide form mature peptide region(mLEAP2), which is responsible for biological activity of the LEAP2 antibacterial peptide. The present study focused on the mLEAP2 for channel catfish. Recombinant DNA expression of the mLEAP2 in Pichia pastoris was realized by constructing P. pastoris expression system. The optimized expression conditions were as follows:29℃, pH 6, 250 r/min, 0.5% methanol and 120 h. Tricine-SDS-PAGE analysis indicated that the expressed product was highly purified by immobilized metal affinity chromatography(IMAC). The concentration of the purified product was 0.22 mg/mL, thus the expression yield of recombinant protein was calculated to be about 2.2 mg/L. Structure of the purified product was further identified by MALDI-TOF/TOF analysis, and the result demonstrated that the purified product was the recombinant mLEAP2(rmLEAP2) expected. In addition, antibacterial assay showed that the fermentation supernatant containing the rmLEAP2 had bacteriostatic activity against Bacillus subtilis.