Abstract: Two antimicrobial peptides were purified from Penus chinensis by Sephadex G-50 gel filtration and reverse phase high performance liquid chromatography. The molecular weights were 1 071 and 1 311 Da respectively, determined by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. They inhibited the growth of Gram-positive and Gram-negative bacteria. The antimicrobial peptides strengthened the contractile response of isolated mice ileum. Serine proteases did not affect hydrolytic activities in our current experiments. These antimicrobial peptides play an important role in preventing microbial infection in P. chinensis.