NRS1 is a murine squamous cell carcinoma that constitutively expresses the co‐stimulatory molecule CD80 at a high level yet grows as a tumour in syngeneic C3H mice. We examined the effect of gene transfer of the 4‐1BB ligand (4‐1BBL) into NRS1 cells. Introduction of the 4‐1BBL gene efficiently elicited anti‐tumour immune responses in syngeneic mice which acquired specific immunity against wild‐type tumour. T‐cell depletion studies showed that CD8⁺, but not CD4⁺ T cells were essential for tumour eradication. Our results suggest that the transduced 4‐1BBL is more effective than the spontaneously expressed CD80 for generation of primary anti‐tumour CD8⁺ T‐cell responses. In addition to CD80 and CD86, the host‐derived 4‐1BBL is also involved in the secondary anti‐tumour responses. This study indicates the complicated contribution of 4‐1BBL, CD80 and CD86 on tumour and host cells in anti‐tumour immune responses and a possible therapeutic application of 4‐1BBL for human tumour vaccination and gene therapy.