Gene therapy offers the possibility of new approaches to cancer treatment. The purpose of this study was to test the feasibility of suicide gene therapy for oral cancer. The human oral squamous cell carcinoma cell line HSC-4 was infected in vitro with recombinant adeno-associated virus (AAV) containing the LacZ marker gene. Expression efficiency of the LacZ gene was 26.9±1.74% at an MOI of 2000 and 100±0% at an MOI of 20000. The HSC-4 cell line was then infected with AAV containing the herpes simplex virus thymidine kinase (HSV-tk) gene and was incubated with ganciclovir (GCV). Transfection of HSV-tk gene and administration of GCV distinctly promoted tumor cell killing. In addition, a bystander effect was demonstrated in vitro. These results suggest that AAV-tk vector may be useful for gene therapy against oral squamous cell carcinoma in humans.