Abstract: To explore the highly-efficient method of purifying antibacterial peptides from the small intestine of duck and antibacterial activities of the antibacterial peptides, the mucous membrane of small intestine had been cracked, heated and lixiviated from 5% acetic acid, and then after ultra-filtration and Sephadex G50 gel filtration chromatography, collected to detect bacteriostatic activity by agarose dispersion method.The samples were also analyzed by Tricine SDS-PAGE dying to determine the molecular weight of the main antibacterial peptides.The results showed that the improved acetic acid purifying method was useful.The bound of molecule weight was 5ku upwards, and the main molecule weight was about 6.5ku.It was strongly against all the bacteria strains mentioned above, such as Escherichia coli, Salmonella and Staphyloccocus aureus.