Relapses occurring in most patients with lymphoma after antibody or chemotherapy highlight a need for effective vaccination approaches. Autologous tumors are ideal sources of patient-specific tumor antigens for vaccines; however, their poor immunogenicity has been a major obstacle in practice. Natural killer T (NKT) cells have recently emerged as crucial regulators of autoimmunity and tumor immunosurveillance. Here, we show that an autologous lymphoma vaccine that activates NKT cells generated tumor-specific protective immunity in experimental mice. Single vaccination with alpha-galactosylceramide (alphaGC)-loaded A20 lymphoma cells elicited effective antitumor immunity against tumor challenge. This vaccination strategy also induced significant tumor regression in A20-bearing mice. Importantly, the survivors from primary tumor inoculation were all resistant to tumor rechallenge, indicative of established adaptive memory immunity. Depletion as well as adoptive transfer studies revealed an exclusive role of conventional CD4(+) but not CD8(+) T cells in mediating antitumor immunity. In addition, we found normal hematopoietic compartments in the vaccinated mice. Therefore, NKT ligand-loaded lymphoma elicits long-lasting and effective antitumor immunity, which can be further developed as patient- and tumor-specific immunotherapy against human lymphomas.