Host immune function plays a certain role against the development of renal cell carcinomas (RCCs), but the mechanism is not entirely understood. Human gamma/delta (gamma/delta) T cells defend the body against infection. In this study, we clarify the role of gamma/delta T cells in the surveillance system against RCCs by analyzing the gamma/delta T cells in peripheral blood mononucleocytes (PBMs) and tumor infiltrating lymphocytes (TILs) from 41 patients with RCCs. The results showed that the number of gamma/delta T cells expressing V gamma 2 and V delta 2 in variable elements of TCR was elevated in the PBMs in 10 patients, but not in any of 32 healthy individuals. The proportion of patients with an elevated number of gamma/delta T cells (> 10%) increased with cancer stage. The level of the gamma/delta T cells decreased after surgery. The gamma/delta T cells in the TILs were more activated than those in the PBMs. Evaluation of the junctional diversity of TCR V gamma 2 and V delta 2 chains showed that the increased peripheral blood gamma/delta T cells were oligoclonal rather than polyclonal. Taken together, our findings suggest that gamma/delta T cells recognize certain RCC-related antigens and play a role in the surveillance system against RCCs.