Amodiaquine (ADQ), an antimalarial drug used in endemic areas, has been reported to be associated with liver toxicity; however, the mechanism underlying its hepatoxicity remains unclear. In this study, we examined the cytotoxicity of ADQ and its major metabolite N-desethylamodiaquine (NADQ) and the effect of cytochrome P450 (CYP)-mediated metabolism on ADQ-induced cytotoxicity. After a 48-h treatment, ADQ and NADQ caused cytotoxicity and induced apoptosis in HepG2 cells; NADQ was slightly more toxic than ADQ. ADQ treatment decreased the levels of anti-apoptotic Bcl-2 family proteins, which was accompanied by an increase in the levels of pro-apoptotic Bcl-2 family proteins, indicating that ADQ-induced apoptosis was mediated by the Bcl-2 family. NADQ treatment markedly increased the phosphorylation of JNK, extracellular signal-regulated kinase (ERK1/2), and p38, indicating that NADQ-induced apoptosis was mediated by MAPK signaling pathways. Metabolic studies using microsomes obtained from HepG2 cell lines overexpressing human CYPs demonstrated that CYP1A1, 2C8, and 3A4 were the major enzymes that metabolized ADQ to NADQ and that CYP1A2, 1B1, 2C19, and 3A5 also metabolized ADQ, but to a lesser extent. The cytotoxicity of ADQ was increased in CYP2C8 and 3A4 overexpressing HepG2 cells compared to HepG2/CYP vector cells, confirming that NADQ was more toxic than ADQ. Moreover, treatment of CYP2C8 and 3A4 overexpressing HepG2 cells with ADQ increased the phosphorylation of JNK, ERK1/2, and p38, but not the expression of Bcl-2 family proteins. Our findings indicate that ADQ and its major metabolite NADQ induce apoptosis, which is mediated by members of the Bcl-2 family and the activation of MAPK signaling pathways, respectively. Published by Elsevier Ltd.