Chronic hepatitis B virus (HBV) infection is the most common cause of hepatocellular carcinoma (HCC) worldwide. This study investigated the antineoplastic effects of intrinsic and extrinsic peroxisome proliferator-activated receptor gamma (PPARgamma) ligands against HBV-associated HCC cells in vitro. Four cell lines that were established from patients with HBV-associated HCC were used. The cells were cultured in various concentrations of the following PPARgamma ligands: troglitazone, pioglitazone, rosiglitazone and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)). Cell proliferation, cell cycle and apoptosis were analyzed. PPARgamma was expressed in all the cell lines studied. Among the PPARgamma ligands, pioglitazone and 15d-PGJ(2) clearly inhibited the HBV-associated HCC cell growth and increased the proportion of cells in the sub-G1 phase in the cell-cycle analysis. In apoptosis assays, DNA fragments increased significantly, and the activities of caspase-3 and -9 also increased. A pan-caspase inhibitor and a caspase-3 inhibitor suppressed the PPARgamma ligand-induced apoptosis in a dose-dependent manner. These two PPARgamma ligands decreased the expression of bcl-2 in most of the cell lines studied. The results suggest that pioglitazone and 15d-PGJ(2) have antineoplastic effects on HBV-associated HCC cells. Both of these PPARgamma ligands could be candidates for cancer prevention or the chemotherapy of HBV-associated HCC.