Aims: A survey was conducted on the ecological distribution of bacteriocin-producing lactic acid bacteria in Miso-pastes, a typical fermented food in Japan. Method and Results: Nine Miso-pastes were sampled for isolation of bacteriocin-producers. Almost all isolated enterococcal strains produced bacteriocins but no isolated tetragenococci did so. The bacteriocin-producing isolates were divided into nine groups by phenotypic tests. As the phenotypic characters were highly diverse, these strains could not be identified to species level on the basis of their phenotypes. The nine representative strains from each group were identified by 16S rRNA analysis. These bacteriocin-producers with one exception (Lactococcus sp.) were identified as strains of the Enterococcus faecium 'species group'. The bacteriocins of the nine strains were classified into five types according to their antibacterial spectral patterns and their SDS-PAGE profiles. The bacteriocins inhibited undesirable bacteria in Miso-pastes, such as Bacillus subtilis, but did not inhibit the useful Tetragenococcus halophila. Conclusions: The bacteriocin-producing lactic acid cocci were widespread at high frequencies in Miso-pastes. They were considered to play an important role in preventing the growth of undesirable bacteria. Significance and Impact of the Study: This study suggests that bacteriocin-producers act effectively as safe biopreservatives and may contribute to the biopreservation in Miso-pastes.