We have investigated the effect of glycyrrhetic acid (GR) which is metabolic substance of glycyrrhizin, on DNA of human hepatoma (HLE), promyelotic leukemia (HL-60) and stomach cancer (KATO III) cells. GR displayed apoptotic effects against HLE, HL-60 and KATO III cells. The fragmentation of DNA by GR to oligonucleosomal-sized fragments, a characteristic of apoptosis, was dose-and time-dependent in these cell lines. These findings suggest that growth inhibition of these cell lines by GR result from the induction of apoptosis by the compound. Inhibitors of caspases did not suppress the DNA fragmentation caused by GR. N-acetyl-L-cysteine, an antioxidant drug, weakly inhibited the DNA fragmentation caused by GR suggesting that active oxidants work partly as an apoptosis-inducing transfer substance.