The activities of antibacterial peptides (ABP) extracted from pig small intestine against 11 strains of bacteria were tested by agarose diffusion assay and live bacteria counting assay. The results showed that the ABP killed or inhibited all tested bacteria strongly except E.coli O_2 and S.typhisuis isolated from an ill pig, and the bacteria-killing rates varied from 59.5% to 98.5%. Scanning electron microscopy of S.pullorum C79-13, E.coli C83845 and S.aureus ATCC25923 treated with the ABP showed considerab...