Two new fermentation products were separated from cheonggukjang by high performance liquid chromatography (HPLC) and tentatively identified as succinyl daidzin and succinyl genistin by HPLC-mass spectrometry (MS). Both succinyl daidzin and succinyl genistin were detected in all 4 commercially available and one laboratory prepared cheonggukjang and 1 commercially available natto. However, these compounds were not detected in commercially available 4 home-made and 4 factory-produced doenjang. Peak areas of succinyl genistin were about 1.95-2.45 times higher than those of succinyl daidzin in cheonggukjang, which may be due to the higher concentration of genistin derivatives than daidzin derivatives in soybeans. This is the first report on the succinyl derivatives as isoflavone metabolites from cheonggukjang and these 2 isoflavone derivatives could be characteristic indicators for cheonggukjang.