Although Lactococcus is one of the most extensively studied lactic acid bacteria, little information is available on the regulation of the catabolite receptor protein (CRP) and acid induced gene expression. The rcfB gene, encoding RcfB protein which has unknown function in Lactococcus lactis IL1403, was analysed. Promoter region contains consensus CRP binding site and acid inducible sequence at upstream of start site. A 402 bp rcfB promoter was fused to upstream of b-galactosidase gene by cloning into promoterless pAK80 plasmid. Promoter activity corresponding to b-galactosidase was measured from Lactococcus lactis IL1403 transformant grown in medium M17 containing different carbon sources. We have found that the rcfB promoter expression was highly induced by acidity and carbohydrate sources used in medium and growth phase of the culture.