Abstract: To evaluate the mechanism of 2-methyl-3-hydroxy-anthraquinone (MHA) inducing apoptosis in human MCF-7 breast cancer cells.Cell viability was assessed by trypan blue dye exclusion assay,cell cycle distribution,apoptosis and mitochondrial membrane potential and Ca²⁺_i were measured by FACScan;the protein expression of caspase-4,caspase-7,caspase-9,Bcl-2,Bax,calpain and cytochrome C in the MCF-7 cells was evaluated by Western blots.The results demonstrated that MHA was able to inhibit cell proliferation in a time-dependent manner.It inducedCa²⁺_i overload, decreased mitochondrial membrane potential and finally induced cancer cell apoptosis.Caspase-4, caspase-7, caspase-9 and calpain protein were activated.Bax expression was upregulated and Bcl-2 expression was downregulated.MHA induced MCF-7 cells apoptosis via Ca²⁺ /calpain/caspase-4 pathway.