Isoliquiritigenin, which is possibly a principal anti-tumor constituent of licorice, a traditional Chinese herb, was examined for apoptosis-inducing activity in human gastric cancer MGC-803 cells. Typical morphological and biochemical features of apoptosis including cell shrinkage, chromatin condensation, DNA ladder formation, and appearance of apoptotic peaks (subG(1)) were observed in MGC-803 cells with isoliquiritigenin treatment. Using Fluo-3 and Rh123 as fluorescent probes, respectively, it was found that the intracellular free calcium concentration increased and the mitochondrial transmembrane potential (Deltapsi(m)) decreased in a dose-dependent manner in apoptotic cells. These results suggest that isoliquiritigenin induced apoptosis of MGC-803 cells through calcium- and Deltapsi(m)-dependent pathways, indicating that it is potentially useful as a natural anti-cancer agent.