Objective: The neutrophil-to-lymphocyte ratio (NLR) and the platelet-to-lymphocyte ratio (PLR) are markers of systemic inflammation. NLR and PLR can predict the treatment outcomes of metastatic cancer for patients treated with immune checkpoint inhibitors (ICI). In this study, we investigated whether NLR or PLR is a better predictor of survival outcomes. Material and Methods: Between February 2016 and November 2021, 106 patients who had metastatic disease arising from different types of solid tumors treated with ICIs were retrospectively evaluated. The cut-off values of the NLR and PLR were determined by performing ROC curve analysis. Cox regression analysis was performed to evaluate the predictive role of NLR and PLR in progression-free survival (PFS). Results: The median age of patients was 62 years (range: 19-84 years), and 60.4% of patients were male. The cut-off values for NLR and PLR were 4.06 and 192.59, respectively. The patients were divided into two groups (low/high) according to the cut-off values. The results of the univariate analysis showed that PFS was significantly longer in the group with low NLR and PLR. High NLR [hazard ratio: 1.95, 95% confidence interval (CI): 1.20-3.15, p=0.006] and ≥2 Eastern Cooperative Oncology Group performance status (hazard ratio: 2.62, 95% CI: 1.61-4.26, p<0.001) were independent negative predictive factors for PFS in the multivariate Cox regression analysis. Conclusion: We found that PFS and disease control rate were significantly better in patients with low NLR who were administered immunotherapy. NLR may be a better predictive marker than PLR in cancer patients administered immunotherapy.