Antioxidant, antiproliferative and apoptosis inducing activities of a natural polyphenolic compound, ellagic acid, were studied. DPPH radical scavenging and lipid peroxidation inhibitory activities were observed. Activities of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) were measured in ellagic acid-treated V79-4 cells. For apoptotic inducing activity, human osteogenic sarcoma (HOS) cell proliferation, chromosomal DNA degradation and changes in apoptosis-related protein levels were measured. Ellagic acid showed high DPPH radical scavenging and lipid peroxidation inhibition activities. SOD, CAT and GPX activities were significantly increased in ellagic acid-treated V79-4 cells. Ellagic acid significantly reduced HOS cell proliferation, and induced apoptosis evidenced by chromosomal DNA degradation and apoptotic body appearance. Bax expression was induced and caspase-3 was activated by ellagic acid treatment. Ellagic acid exhibited both antioxidant activity in V79-4 cells and apoptosis-inducing activity in HOS cells through the up-regulation of Bax and activation of caspase-3.