The researches on antibacterial peptides from Mytilus coruscus, an important Mytilus in aquaculture, have significant value helping people to understand the mechanism of innate immune system of this mussel. Here, three peptides with antibacterial activity were purified from Mytilus coruscus serum by multidimensional high performance liquid chromatography(HPLC). The three peptides exhibited complementary antimicrobial properties against both grampositive and gramnegative bacteria. The mass and the Nterminal sequences of these peptides were analyzed by a combination of Edman degradation and Mass Spectrometry. Based on the results of sequential BLAST, these antibacterial peptides from Mytilus coruscus serum belong to Mytilin family and are named Mytilin1, Mytilin2 and Mytilin3, respectively; The molecular mass of these antibacterial peptides are 3885.17 u，3993.26 u and 3991.39 u, respectively. Among them, Mytilin1 was characterized as a 34residues peptide including eight cyctines formed four disulfides. The cDNA sequence coding for the Mytilin-1 precursor was obtained by screening PCR from the cDNA library of Mytilus coruscus blood cell. The precursor of Mytilin-1 contains a putative signal peptide of 22 residues, a processing peptide sequence of 34 amino acids, and a Cterminal extension of 46 residues rich in acidic residues. This study lays the foundation for further research about the molecular diversity and the mechanism of these antibacterial peptides from Mytilus coruscus serum.