Objective:To investigate the clinical value of peripheral monocyte and neutrophil count in predicting the response of patients with metastatic non-small cell lung cancer (mNSCLC) to immunosuppressive checkpoint inhibitors (ICI).Methods:The clinical data of 34 adult mNSCLC patients who received nafulizumab or pabolizumab in Danzhou People's Hospital of Hainan Province from January 2017 to March 2019 were retrospectively analyzed. The correlation of the demographic characteristics, clinical data, hematological examination results in the first two weeks before the treatment and two weeks after ICI treatment with prognosis was recorded and observed.Results:The baseline mean monocyte count [(0.52±0.09)×10 9/L vs. (0.60±0.12)×10 9/L] and neutrophil count [(4.27±0.87)×10 9/L vs.(5.39±1.02)×10 9/L] of patients with ICI reaction were lower than those of patients without ICI reaction, and the differences were statistically different ( t = -2.572, -2.727, all P < 0.05). However, there was a negative correlation between the monocyte count of the patients who responded to ICI and the reaction time ( r = -0.507, P < 0.05). The median reaction time in patients with monocyte count >0.70×10 9/L was shorter than that in patients with monocyte count ≤0.70×10 9/L (8 weeks vs. 12 weeks, χ2=4.162, P = 0.041). There was no correlation between monocyte count and time of reaction duration, progression of free survival (PFS) and overall survival (OS) ( r = -0.214, 0.182, 0.232, all P > 0.05). The decrease rate of neutrophil count in response group was higher than that in non-response group (22% vs. 2%, P < 0.05). After the first administration, cutoff value of neutrophil count was 4.2×10 9/L; the response rate of patients with neutrophil count ≤ 4.2×10 9/L was higher than that of patients with neutrophil count > 4.2×10 9/L [86.7% (13/15) vs. 36.8% (7/19), χ2=6.657, P < 0.05]. Conclusion:Peripheral blood monocyte and neutrophil count can predict the response to ICI therapy in patients with mNSCLC.