Ginsenosides, ginseng saponin, are the principal components responsible for the pharmacological and biological activities of ginseng. In order to improve absorption and biological activities, the biotransformation of major ginsenoside to minor ginsenoside, as the more active compound, is required. In this study, we isolated Lactobacillus brevis THK-D57, which has high β-glycosidase activity, from Kimchi. The major ginsenoside Rb₁ was converted to the minor ginsenoside ‘compound K’ during the fermentation of L. brevis THK-D57. The results propose that the biotransformation pathway to produce compound K is as follows: ginsenoside Rb₁→ginsenoside Rd→ginsenoside F₂→ginsenoside compound K.