Five hundreds of bifidobacteria were isolated from a healthy Korean and the inhibitory effects of these isloated bacteria on harmful enzymes of human intestinal microflora were examined by cocultivation of the isolated bifidobacteria with E. coli or total human intestinal microflora. In comparison with the results of E. coli or intestinal microflora cultivation, Bifidobacterium breve K-110, B. breve K-111 and B. infantis K-525 effectively inhibited harmful enzymes ($eta$-glucuronidase and tryptophanase) of E. coli and lowered the pH of the culture media. Also they inhibited the harmful enzymes ($eta$-glucosidase, $eta$-glucuronidase, tryptophanase and urease) and ammonia production of intestinal microflora, and lowered pH of the culture media by increasing lactic acid bacteria of intestinal microflora. When these isolated bifidobacteria were administered on mice, fecal harmful enzymes were also inhibited. Among tested bifidobacteria, B. breve K-110 had the highest inhibitory effect of fecal harmful enzymes.