Program cell death-1 (PD-1) blockade treatment has been shown effective in cases with relapsed/refractory classical Hodgkin Lymphoma (R/R cHL), while prognostic biomarkers remain unclear. Seventy-seven cases with R/R cHL who received immunotherapy for the first time were included. Receiver operator characteristic analysis displayed platelet-to-neutrophil ratio (PNR) as the most probable indicator among distinct inflammatory-cell ratios. Patients with high pretreatment PNR (≥ 51.6) achieved significantly higher complete response (CR) rate as compared with patients with low PNR (< 51.6), and PNR patients displayed significantly longer progression-free survival (PFS) versus PNR patients ( = 0.001). Cox analysis indicated PNR as an independent factor for prognosis (hazard ratio, 0.34, 95% CI, 0.18-0.65, = 0.001). Among patients acquiring CR, higher PNR was associated with improved PFS and relapse-free survival. Moreover, PNR correlations with CR rate and PFS were validated in external cohort of cHL. Notably, PNR was also a strong prognostic biomarker for PFS and overall survival after anti-PD-1 combination therapy in patients with solid tumors, such as biliary tract carcinoma, gastric carcinoma, or colon cancer. In conclusion, this study for the first time reveals a correlation between pretreatment peripheral PNR and prognosis of anti-PD-1-based therapy in patients with relapsed/refractory cHL and advanced solid tumor.