Cadmium (Cd) is an important industrial and environmental pollutant. In animals, the liver is the major target organ of Cd toxicity. In this study, rat hepatocytes were treated with 2.5∼10μM Cd for various durations. Studies on nuclear morphology, chromatin condensation, and apoptotic cells demonstrate that Cd concentrations ranging within 2.5∼10μM induced apoptosis. The early-stage marker of apoptosis, i.e., decreased mitochondrial membrane potential, was observed as early as 1.5h at 5μM Cd. Significant (P < 0.01) reactive oxygen species (ROS) production at 5μM Cd and 0.75h occurred prior to the decrease of the mitochondrial membrane potential, suggesting the involvement of ROS in mitochondrial membrane damage. Glutathione (GSH) level significantly decreased after cell treatment with 5 and 10μM Cd after 12h (P < 0.01). Meanwhile, the intracellular free Ca(2+) concentration ([Ca(2+)] i ) of Cd-exposed cells significantly increased (P < 0.01) at 1.5h, and pretreatment with the calcium chelator Bapta-AM partially blocked Cd-induced apoptosis. This finding indicated that the elevation of [Ca(2+)] i may play an important role in apoptosis. Overall, these results showed that oxidative stress and Ca(2+) signaling were critical mediators of the Cd-induced apoptosis of rat hepatocytes.