Interferon-gamma (IFN-γ) exhibits biological activities that are considered to have important roles in tumor suppression. Therefore, the IFN-γ gene is a potential candidate for in vivo cytokine gene therapy against skin cancer. The present study evaluated the efficacy of a hydrodynamics-based IFN-γ gene transfection for skin cancer treatment, in which the plasmid DNA encoding IFN-γ was administered into the tail vein of mice following 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate-induced skin carcinogenesis. Serum levels of IFN-γ were substantially elevated without liver toxicity. The mice injected with IFN-γ plasmid DNA displayed a marked reduction in papilloma numbers, suppressed proliferation of epidermal cells and induction of caspase-3-mediated apoptosis. These results suggest that the hydrodynamics-based transfection of IFN-γ plasmid DNA is a convenient and efficient means of skin cancer gene therapy.