This study was undertaken to investigate the inhibitory effects of propolis on the in vitro proliferation of human colon(HT-29) and hepatoma(HepG2) cancer cell lines. The growth of the HT-29 and HepG2 cells was respectively inhibited by the administration of propolis in a concentration response-dependent manner. The distributions of HT-29 and HepG2 cells cultured in the medium containing propolis were shifted to the smaller sizes, and then HT-29 and HepG2 cells were shrunken under microscopic observations. The progression of cell cycle from G1 to S phase was significantly inhibited by propolis in the HT-29 and HepG2 cell lines, respectively. Those observations suggest that propolis has anticancer effect against some of cancer cell lines in vitro. (Korean J Nutrition 33(1) : 80-85, 2000)