Recently, dendritic cells (DC) transfected with tumor RNA have been used as a cancer vaccine. The efficacy of a cancer vaccine using DC transfected tumor RNA was examined. Of particular interest was whether a vaccine using DC transfected with recrudescent tumor RNA is effective for the treatment of a regrowing tumor after prior immunotherapy. In addition, the usefulness of co‐transfection of granulocyte macrophage colony‐stimulating factor (GM‐CSF) mRNA to augment the DC vaccine was examined. CT26 tumor‐bearing mice were immunized by s.c. injection with DC transfected with CT26 mRNA (DC‐CT26). The cytotoxic activity against CT26 in mice immunized with DC‐CT26 was significantly higher than that in the control group (P < 0.001) and was augmented by GM‐CSF mRNA co‐transfection (P < 0.05), resulting in remarkable therapeutic efficacy in CT26 s.c. tumor models. Cytotoxic T lymphocytes induced by the vaccination using DC transfected with mRNA from the recrudescent tumor showed a potent cytotoxicity against the recrudescent CT26 tumor cells, which was significantly higher than the cytotoxicity induced by the vaccination using DC‐CT26 (P < 0.05). In addition, in a recrudescent tumor model, this vaccination suppressed the regrowing s.c. tumors, and was augmented by GM‐CSF mRNA co‐transfection (P < 0.05). These results suggested that vaccination therapy using DC simultaneously transfected with whole tumor RNA and GM‐CSF mRNA could generate therapeutic immune responses even against recrudescent tumor after prior vaccination. (Cancer Sci 2008; 99: 407–413)