Objective: We investigated the prognostic and predictive effects of the ABO blood group system on patients receiving immune checkpoint inhibitors for advanced renal cell carcinoma (RCC). Material and Methods: In this retrospective observational study, the data on the patients with known ABO blood group, who were administered nivolumab for mRCC, were reviewed. The tumor response rates and survival were analyzed based on the ABO blood group. Results: A total of 89 patients were included in the study. The median age of the patients was 57 (range: 24-83 years) years, and 67% (n=60) of the patients were male. Moreover, 43%, 18%, 9%, and 30% of the patients had blood groups A, B, AB, and O, respectively. Our study had a median follow-up time of 11 months. Although the groups did not differ significantly in progression-free survival (PFS) and overall survival (OS) according to the blood groups, patients who had the B blood type survived longer. For patients with blood types A, B, AB, and O, the median PFS was 5.3 months, 8.4 months, 3.7 months, and 7.8 months, respectively (p=0.8), and the median OS was 14.5 months, 20.3 months, 12.0 months, and 16.5 months, respectively (p=0.8). Conclusion: Although the groups did not differ significantly according to the ABO blood group, the patients with the B blood group survived relatively longer. These results suggested that further studies with more patients should be conducted.