The objectives of this study were to isolate various isoflavone fractions and extracts from soybean cake by preparative column chromatography and compare them with isoflavone standards with regards to inhibition of HepG2 cancer cell proliferation. Four fractions, including malonylglucoside, glucoside, acetylglucoside and aglycone, and two isoflavone extracts, ISO-1 and ISO-2, were collected for evaluation. MTT test results showed that most treatments were slightly protective against HepG2 cell growth at a low dose of isoflavone ( 5 and 10 mu g/mL). However, at elevated concentration of isoflavone (20-50 mu g/mL), both aglycone and acetylglucoside fractions as well as a mixture of isoflavone standards were the most effective in inhibition, demonstrating a possible synergistic phenomenon. Genistein showed a better retardation effect than daidzein. For cell cycle analysis, both aglycone and acetylglucoside fractions and a mixture of isoflavone standards exhibited a high G2/M ratio, correlating well with the result of MTT test. The presence of some other functional components in soybean cake like saponins and phenolic compounds may also play a vital role in inhibiting HepG2 cell growth.