We have investigated the effects of rhapontin on proliferation and DNA of human stomach cancer KATO III cells. Growth inhibition and induction of apoptosis by rhapontin were observed in the KATO III cells. Morphological change showing apoptotic bodies was observed in the KATO III cells treated with rhapontin. The fragmentation of DNA by rhapontin to oligonucleosomal-sized fragments that is a characteristic of apoptosis was observed to be concentration- and time-dependent in the KATO III cells. N-acetyl-L-cysteine, an antioxidant, suppressed the DNA fragmentation caused by rhapontin. On the other hand, it was found that resveratrol having stilbene moiety as well as rhapontin induced apoptosis in the KATO III cells. So, it is considered that stilbene moiety in the molecule is essential for the induction of apoptosis. The data of the present study show that the suppression of KATO III cell-growth by rhapontin results from the induction of apoptosis by the compound, and that active oxygen is involved in the inductions of apoptosis caused by rhapontin in the KATO III cells.