Gene therapy is a promising strategy for cancer treatment. The strategy is categorized to some fields based on the anti-cancer mechanism. p53 gene therapy and antisense therapy exert the cytotoxic effect on cancer cells by apoptosis induction. In suicide gene therapy, expressed suicide gene product kills the cancer cells in combination with prodrug which metabolite is cytotoxic agent. Oncolytic virus replicates in the tumor selectively and destroys the cancer cells. Immunogene therapy potentiates the antigenicity of cancer cells or activate the immune effector cells. In antiangiogenesis gene therapy, neovascularization is inhibited with antiangiogenic molecule gene such as angiostatin. On the other hand, bone marrow stem cells are protected from high dose anti-cancer agents by the transfer of multi-drug resistant gene.