Non-small cell lung cancer (NSCLC) is one of the important causes of cancer-related mortality worldwide. Previous studies have demonstrated the crucial roles of mucosal-associated invariant T (MAIT) cells in regulating tumor immunity, while their roles in NSCLC remain largely unknown. The aim of this study is to evaluate clinical relevance of MAIT cells in blood and tumor tissues of patients with NSCLC. Here, we find that there is no significant difference in the frequency of circulating MAIT cells between NSCLC patients and healthy donors. However, the MAIT-frequency is significantly declined in lung tumor tissues compared to their peri-tumor counterparts, which relates to Tumor-Node-Metastasis (TNM) stage. The MAIT-frequency in lung tumor tissues is higher in node-negative patients compared to node-positive patients. Furthermore, tumor-infiltrating MAIT cells display a tissue-resident effector-memory phenotype and exhibit upregulated levels of exhaustion markers. The percentage of tissue-resident cells in MAIT tends to be higher in tumor tissues than in peri-tumor tissues. In addition, the percentage of IL-17A+ MAIT cells is significantly higher in lung tumor tissues than that in peritumor tissues. In summary, our results indicate the possible detrimental role of MAIT cells in the development and progression of NSCLC.