AIM: To study the anti-neoplastic effect of Haimiding and its mechanisms of action.METHODS: Experiments using MTT and colony formation were carried out to study thein vitro anti-neoplastic action of Haimiding, its in vivo anti-neoplastic action was studied by observing its effect on the weight of tumors in FC mice and S180, H22 tumor bearing mice, as well as their life spans.The effect of Haimiding on cell apoptosis and different stages of cell cycles in human gastric carcinoma cells were studied by flow cytometry. Its effect on [Ca2+]i of human gastric carcinoma cells and the source of Ca2+ during the change of [Ca2+]i were observed by confocal laser scanning technique.RESULTS: Haimiding showed a definite cytotoxicity to 8 human tumor cell lines, which was most prominent against BGC-823, Eca-109 and HCT-8 tumor cells. It also exhibited an obvious inhibition on colony formation of the above tumor cell lines, which was most prominent in Eca-109 tumor cells. It showed obvious inhibition on the growth of tumor in FC mice and S180 bearing mice as well as prolonged the life span of H22 bearing mice. It was able to induce apoptosis and elevate intracellular [Ca2+]i concentration of tumor cells.The source of Ca2+ came from both extracellular Ca2+ influx and intracellular Ca2+ release.CONCLUSION: Haimiding is composed of a TCM preparation and 5-flurouracil. Its anti-neoplastic potency is highly enhanced by synergism as compared with either one of its components. Its mechanisms of anti-neoplastic action can be attributed to its action to initiate apoptosis of tumor cells by opening the membrane calcium channel and inducing intracellular Ca2+ release to elevate [Ca2+]i of the tumor cells.