We have investigated the effects of three types of procyanidin isolated from apple (Rosaceae Malus pumila) on DNA of human stomach cancer KATO III cells. Induction of apoptosis by these procyanidins was observed in human stomach cancer KATO III cells. Morphological changes showing apoptotic bodies were observed in the KATO III cells treated with procyanidins. The fragmentation of DNA by procyanidins to oligonucleosomal-sized fragments, 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 induced by these procyanidins. The present study shows that the suppression of KATO III cell-growth by three types of procyanidin results from the induction of apoptosis by these compounds, and that active oxygen is involved in the induction of apoptosis by these compounds in the KATO III cells.