Arsenic trioxide (As(2)O(3)), an ingredient in many traditional Chinese medicines, has drawn broad attention due to its therapeutic effects on a variety of cancers, including some solid tumors. However, the effects of As(2)O(3) on cholangiocarcinoma have not been reported. In the present study, we demonstrate for the first time that clinically obtainable concentrations of As(2)O(3) inhibit cell growth and induce apoptosis in human cholangiocarcinoma SK-ChA-1 cells. As(2)O(3)-induced apoptosis was partially inhibited by caspase inhibitor and accompanied by changes in the expression of Bcl-2 family proteins, decrease of mitochondrial membrane potential (MMP), release of cytochrome C from mitochondria, activation of caspase-3, caspase-9, and cleavage of poly (ADP-ribose) polymerase (PARP). Thus As(2)O(3) induces apoptosis in SK-ChA-1 cells via mitochondria-mediated, caspases-dependent pathways. As(2)O(3) inhibition of Akt phosphorylation may contribute to As(2)O(3)-mediated cholangiocarcinoma cell growth inhibition and apoptosis induction.