Background: Programmed death ligand 1 (PD-L1) expression is not truly reflected response of immunotherapy. Thus, tumor mutational burden is new biomarker for predict response of immunotherapy. However, sufficient quantity or quality tumor samples must be obtained, so this is limitation. Therefore, we investigated whether high serum absolute lymphocyte count (ALC) is predictive biomarker for immunochemotherapy response regardless of PD-L1 immunohistochemistry stain among lung cancer patients. Materials and Methods: We retrospectively analyzed the medical charts of lung cancer patients who treated with immunotherapy (pembrolizumab, nivoluamb, ipilimumab, atezolizumab) at Seoul National University Hospital between April 2016 and March 2019. We evaluated correlation the serum absolute lymphocyte count (ALC) with the progression free survival (PFS) using cox proportional hazard model. ALC at before and after one month of immunotherapy was collected. ALC are presented as medians with interquartile ranges (IQRs). Quartile group of ALC was compared using Kruskal-Wallis statistical test. Results: Total 236 patients treated with immunotherapy for lung cancer. Median follow up period was 4.7 months. During the period, 137 (58.1%) had progression of disease. Progression event was significantly lower for post-treatment ALC Q2-4 than Q1 in our adjusted model (Q4 HR 0.42 95% CI 0.24-0.71, p = 0.001). Overall survival was also showed similar results. Association with total or serious adverse event and ALC was not observed in this study. Conclusion: In this study, we revealed that increased post treatment ALC was associated with favor progression free and overall survival among lung cancer patients who treated with immunotherapy. Therefore, ALC could predict response of immune checkpoint inhibitor for lung cancer patients.