The antitumor effects of curcumin, a natural biologically active compound extracted from rhizomes of Curcuma longa, have been studied in many cancer cell types including human hepatocellular carcinoma (HCC). Here, we investigated the effects of Ca(2+) on curcumin-induced apoptosis in human HCC J5 cells. The abrogation of mitochondrial membrane potential (ΔΨ(m)), the increase of reactive oxygen species (ROS) production, and calcium release were demonstrated with flow cytometry as early as 15 minutes after curcumin treatment. In addition, an increase level of cytochrome c in the cytoplasm which led to DNA fragmentation was observed. To verify the role of Ca(2+) in curcumin-induced apoptosis, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), an intracellular calcium chelator, was applied. Cell viability was increased, but ΔΨ(m), ROS production, activation of caspase 3, and cell death were decreased in J5 cells pretreated with BAPTA for 2 h followed by the treatment of 25 μM curcumin. These results suggest that the curcumin-induced apoptosis in human HCC J5 cells is via mitochondria-dependent pathway and is closely related to the level of intracellular accumulation of calcium.