Bu-Zhong-Yi-Qi-Tang (BZYQT), a Chinese herbal medicine, inhibited the proliferation of human hepatoma cell lines (Hep3B, HepG2 and HA22T) dose-dependently. The IC50s of BZYQT on the proliferation of Hep3B, HepG2 and HA22T were 432.5+/-31.8 microg/ml, 455.4+/-24.2 microg/ml, and 2284.3+/-77.2 microg/ml respectively on day 3. However, BZYQT did not significantly inhibit the proliferation of normal human hepatocytes (Chang liver, CCL-13) at the concentration under 5,000 microg/ml. Major compounds of BZYQT, including astragaloside IV, ginsenoside Rb1 and Rg1, saikosaponin a and c, and glycyrrhizin, have been identified. To investigate the key inhibitors of BZYQT. Hep3B cells were treated with BZYQT, individual major compounds of BZYQT, and mixture of major compounds in the same ratio as present in BZYQT. Significant inhibition of proliferation was detected in BZYQT and its major compounds mixture in a comparable level. Not any individual major compound examined could suppress the proliferation of Hep3B cells. This data indicated that there could be synergistic or additive effects of the ingredients in BZYQT. BrdU incorporation, cell cycle analysis and DNA fragmentation assay revealed that BZYQT suppressed the proliferation of hepatoma cells via G0/G1 cell cycle arrest and inhibition of DNA synthesis followed by apoptosis.