Abstract: Objective The aim of this study was to investigate the potential of using plasma exosomal PD-L1 （ePD-L1） as a biomarker for non-small cell lung cancer（NSCLC）. Methods Two NSCLC cell lines, H226 （low-expressed PD-L1） and H1975 （high-expressed PD-L1） and one breast cancer cell line MCF7 （PD-L1 negative） were selected for this study. The exosomes secreted by cells into culture medium were separated by high-speed centrifugation, and the cell lysate was also collected. CD9 was used as a marker for exosomes detection. The exosome-released PD-L1 expression level and the ePD-L1 level were detected by Western Blot. Results H1975 and MCF7 cell lines showed stronger CD9 expression level compared to H226 cell line. H1975 cell line with stronger PD-L1 expression showed higher ePD-L1 level compared to H226 cell line. PD-L1 negative MCF7 cell line was also found to be ePD-L1 negative. Conclusion Plasma ePD-L1 expression is regulated by the expression level of PD-L1 in tumor cells and the secretion level of exosomes from tumor cells. ePD-L1 expression can be an indicator for the expression level of PD-L1 in tumor tissues.