NKT cells, a novel murine lymphoid lineage bearing an invariant T cell receptor encoded by Vα14 and Jα281 gene segments, recognize a specific ligand glycolipid, α‐galactosylceramide (α‐GalCer) in a CDld‐dependent manner. Recent research has revealed that activated Vα14 NKT cells have dramatic antitumor effects against a wide variety of tumor cell lines in vivo and in vitro. Here, we demonstrate strong in vivo antitumor effects brought about by treatment with α‐GalCer‐pulsed dendritic cells in comparison with in vitro‐activated Vα14 NKT cells. Furthermore, we show a significant expansion of endogenous Vα14 NKT cells in the lung following the administration of α‐GalCer‐pulsed dendritic cells. The feasibility of immunotherapy with α‐GalCer‐pulsed dendritic cells is discussed.