The antioxidant activity, cytotoxicity and mechanism of induction of HepG2 cell death of essential oil from Amomum tsao-ko were determined. The essential oil was cytotoxic to HepG2, Hela, Bel-7402, SGC-7901 and PC-3 cell lines. The lowest IC(50) of 31.80 +/- 1.181 mu g/ml was measured for HepG2 carcinoma cell lines. The IC(50) for normal human cell lines (HUVEC and HL-7702) was 163.91 +/- 5.11-272.41 +/- 0.97 mu g/ml. Analyses by flow cytometry. Hoechst 33258 staining and agarose gel electrophoresis indicated that the essential oil induced apoptosis. The essential oil has weak antioxidant activity as measured by 1,1-dipheny1-2-picrylhydrazyl (DPPH) radical assay, thiobarbituric acid (TBA) test and ferric reducing antioxidant power (FRAP) assay. The data suggest that the essential oil of A. tsao-ko could be a potential medicinal resource. (C) 2010 Elsevier Ltd. All rights reserved.