Lactic acid bacteria (LAB) are typical probiotic microbes that are used in various industries including fermented foods, feed additives, and pharmaceuticals. The purpose of this study was to compare the ability of isoflavone biotransformation and antioxidative activity of 17 LAB. Six strains including the Lactobacillus species exhibited a 100% hydrolysis rate for daidzein during fermentation. The content of total genistein in soymilk fermented with these strains was 872-943 μg/g. The DPPH (1, 1-diphenyl-2-picrylhydrazyl) radical scavenging ability of the LAB was widely variable and ranged from 23-78%. A selected strain was isolated from kimchi and the strain was identified as Lactobacillus plantarum ssp. through the API carbohydrate fermentation pattern and 16S rDNA profile. The strain exhibited excellent acid tolerance in an artificial gastric solution. L. plantarum YS712 showed high β-glucosidase activity in fermentation. The concentration of genistein and daidzein in soymilk fermented with L. plantarum YS712 increased from 3.64 to 917.3 μg/g and from 58.18 to 1062.17 μg/g, respectively. These results demonstrate the potential of L. plantarum YS712 as a probiotic culture that can be utilized in the manufacturing of fermentation foods and dietary supplements.