Bacteriocins produced by lactic acid bacteria showing stability even in neutral and weak alkaline pH were screened, and a new bacteriocin produced by Lactobacillus plantarum A-1, plantaricin ASM1 (PASM1) was purified and characterized. This bacteriocin which is heat-stable but digested by trypsin inhibits the growth of lactic acid bacterial species, such as Lactobacillus, Leuconostoc, and Enterococcus. PASM1 showed stability in a wide pH range compared to nisin A. The bacteriocin was purified using cation exchange, hydrophobic interaction, and reverse-phase high-performance liquid chromatography. The activity of the purified bacteriocin was obtained as one fraction. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of the fraction showed a mass of 5045.7Da. Combining the data obtained from amino acid and DNA sequencing, the primary sequence of PASM1 was determined. The sequence of the corresponding gene revealed that the peptide is ribosomally synthesized as a 64 amino acid precursor containing a 21 amino acid N-terminal extension of the double-glycine type. The mature peptide consists of 43 amino acids, which could contain two intramolecular disulfide bonds in the structure. Three putative open reading frames were located upstream of the PLNA1 gene. These genes may encode the thioredoxin family proteins and a response regulator both of which have been suggested to regulate expression of the PASM1 gene and the processing of its leader peptide. PASM1 has no reported homologue bacteriocins. Stability in a wide pH range and heat indicates its potential for application in food preservation.