Background: Immunohistochemistry (IHC) of the PD-L1 protein is a predictive marker for anti-PD-1 and anti- PD-L1 immunotherapy in non-small cell lung cancer (NSCLC). PD-L1 IHC 22C3 pharmDx is the first PD-L1 IHC assays to obtain regulatory approval in KFDA. This assay is able to identify the group of NSCLC patients who will benefit most from treatment with the immune checkpoint inhibitor. Methods: A total of 362 NSCLC samples were tested. Used PD-L1 IHC 22C3 PharmDx kit and Autostainer Link48 (DAKO). Results: On evaluation of tissue criteria according to the tissue acquisition methods, 82.5% (175/212) of PCNB, 68.1% (62/91) of Endobronchial Ultrasound (EBUS) and 100% (53/53) of resection specimen showed more than 100 viable tumor cells; in terms of sample acquisition site, 71.3% (87/122) of samples from lymph node and 86.0 % (148/172) of samples from lung showed more than 100 viable tumor cells. Of the 221 adenocarcinoma cases, 86 (38.9%) showed high expression, 36 (16.3%) showed low expression and 99 (44.8%) showed no expression. Of the 101 squamous cell carcinoma cases, 39 (39.0%) showed high expression, 30 (30.0%) showed low expression and 31(31.0%) showed no expression. In terms of sample acquisition methods, 215 PCNB samples included 68 (32.1%) high expression, 52 (24.5%) low expression and 92 (43.4%) no expression cases. Of the 92 EBUS samples, 40 (44.0%) showed high expression, 11 (12.1%) showed low expression and 40 (44.0%) showed no expression. Of the 53 resection samples, 28 (52.8%) cases showed high expression, 7 (13.2%) cases showed low expression and 18 (34.0%) cases showed no expression. Conclusion: The result of PD-L1 assay can be affected by various factors.