Leuconostoc sp. J2, isolated from naturally fermented Kimchi, produced a bacteriocin which was named leuconocin J. This bacteriocin exhibited an inhibitory activity against several lactic acid bacteria and some food-borne pathogens. The antimicrobial substance was secreted into the medium during the late log phase. It appears to be proteinaceous since its activity was completely inactivated by a range of proteolytic enzymes, and it was also relatively heat-stable. The bacteriocin was partially purified by ammonium sulphate precipitation, following dialysis. The apparent molecular mass of partially purified bacteriocin, as indicated by activity detection after Tricine-SDS-PAGE, was 2·5–3·5 kDa. Leuconostoc sp. J2 plasmid DNA digested by EcoRI was cloned into pUC118 and transformed into Escherichia coli DH5α. Phenotypic expression of the bacteriocin production was detected in transformants harbouring pULBJ5·5. Finally, Southern blotting with the 2·3 kb insert as a probe against plasmid digests of Leuconostoc sp. J2 revealed that the cloned foreign DNA originated from Leuconostoc sp. J2.