Intravesical inoculation of Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been used for the treatment of bladder cancer. Recent studies implied the requirement of neutrophil infiltration for the antitumor effect. In this study, we found that IL-17 was produced in the bladder after BCG treatment, preceding the infiltration of neutrophils. Neutrophils in the bladder after BCG treatment were reduced in IL-17-deficient mice, in which BCG-induced antitumor effect against intravesically inoculated bladder cancer was abolished. Notably, the level of IL-17 production and the number of neutrophils in BCG-treated bladder was reduced in γδ T-cell-deficient mice but not in CD4-depleted mice. Survival of bladder cancer-inoculated γδ T-cell-deficient mice was not improved by BCG treatment. These results suggest that IL-17-producing γδ T cells play a key role in the BCG-induced recruitment of neutrophils to the bladder, which is essential for the antitumor activity against bladder cancer.