Background: The neutrophil-lymphocyte ratio (NLR) is a well-known prognostic marker in various cancers. However, its role as a predictive marker for the effectiveness of nivolumab in patients with metastatic RCC (mRCC) remains unclear. We evaluated the relationships between the NLR and progression-free survival (PFS) or overall survival (OS) in mRCC patients treated with nivolumab. Methods: The data of 46 mRCC patients who received nivolumab therapy were collected from six institutes and evaluated. The median follow-up period from treatment with nivolumab was 12.5 months (IQR 10.0-16.7). Results: The median duration of nivolumab therapy was 6.5 months (IQR 3.3-13.7). The objective response rate was 22% and the 1- and 2-year PFS rates were 49.4% and 34.8%, respectively. The median NLR values at baseline and 4 weeks were 3.7 (IQR 2.7-5.2) and 3.7 (IQR 2.5-5.9), respectively. In the multivariate analysis, an NLR of ≥ 3 at 4 weeks was an independent predictor of PFS (P = 0.005) and OS (P = 0.031). The 1-year PFS of patients with an NLR of < 3 at 4 weeks was better than that of those with an NLR of ≥ 3 (83% versus 27%, P = 0.001). The 1-year OS of patients with an NLR of < 3 at 4 weeks was also better than that of those with an NLR of ≥ 3 (94% versus 71%, P = 0.002). Conclusions: Although the baseline NLR was not associated with PFS or OS, an NLR of ≥3 at 4 weeks after the initiation of therapy might be a robust predictor of poor PFS and OS in mRCC patients undergoing sequential treatment with nivolumab.