Background: MicroRNAs (miRNAs) play a significant role in shaping immune response. The expression profile of miRNAs, however, has been found to be affected by the presence of tumor, but whether the incidence of non-small cell lung cancer (NSCLC) alters the expression profile of miRNAs has not been studied. Objective: The current study aims to investigate the expression of miRNAs in the peripheral blood mononuclear cells (PBMCs) from patients with NSCLC as well as to analyze the numbers of helper CD4⁺ and cytotoxic CD8⁺ T lymphocytes in PBMCs of the same patients as compared to healthy controls. Methods: PBMCs were prepared from blood harvested from early-diagnosed patients with NSCLC (n=10). The gene expression of miRNAs in PBMCs was measured using microarray and the phenotypic analysis of helper CD4⁺ T-cells and cytotoxic CD8⁺ T-cells in PBMCs was determined by flow cytometry. Results: A significant upregulation of miRNA-21 (2-fold) and downregulation of miRNA-155 (-1.5-fold) was observed in the PBMCs of NSCLC patients as compared to healthy controls. The relative and absolute numbers of CD4⁺ and CD8⁺ T-cells were significantly elevated in the PBMCs of NSCLC patients. Conclusion: Our results indicate that both expression levels of miRNA-21 and miRNA-155 in PBMCs and the numbers of CD4⁺ and CD8⁺ T-cells are altered by the presence of NSCLC.