Although gene therapy has been suggested to be a novel strategy to treat hepatocellular carcinoma (HCC), no study showing the clinical feasibility of vectors to treat HCC has been reported. In this preclinical study, we show evidence indicating that hemagglutinating virus of Japan (HVJ) liposomes are a feasible vector to treat HCC in a clinical setting using ganciclovir (GCV) and herpes simplex virus thymidine kinase (HSV-tk), which is driven by the cytomegalovirus immediate early enhancer/promoter (plasmid pcDNA3/HSV-tk). In in vitro experiments, almost complete tumor cell regression was achieved with the optimal GCV concentration (100 microg/mL) and more than 1/3 regression was seen even with a 20% transduction ratio using HuH7 HCC cells stably transformed by HSV-tk. HVJ liposomes showed a 19.7% (mean) transduction rate of the lacZ gene in a relatively large mass of more than 300 mm3 in vivo, which is a clinically detectable size, implanted into SCID mice. Moreover, a single HSV-tk injection of HVJ liposomes followed by GCV treatment inhibited tumor growth at least within a week, and repeat administration was more effective. Furthermore, subcutaneous injection of an HVJ liposomes vehicle induced no apparent inflammatory response in C3H/HeN mice, whereas lacZ gene transfection resulted in inflammatory pathology, suggesting a lower immunogenicity of the HVJ envelope protein than those of bacteria-derived plasmid DNA or the beta-galactosidase gene product. From these findings, we conclude that HVJ liposomes are a clinically safe and effective gene transfer vector to treat HCC.