T-cell tolerance is an important mechanism for tumor escape, but the molecular pathways involved in T-cell tolerance remain poorly understood. It remains unknown whether the inhibitory immunoreceptor programmed death-1 (PD-1) plays a role in conditions of human non-small cell lung cancer (NSCLC). In this study, we detected PD-1 expression on CD8+ T cells from healthy control peripheral blood mononuclear cells (PBMCs) and the PBMCs of NSCLC patients as well as NSCLC tissues. Results showed that tumor-infiltrating CD8+ T cells had increased PD-1 expression and impaired immune function, including reducing cytokine production capability and impairing capacity to proliferate. Blockade of the PD-1/PD-L1 pathway by the PD-L1-specific antibody partially restored cytokine production and cell proliferation. These data provide direct evidence that the PD-1/PD-L1 pathway is involved in CD8+ T-cell dysfunction in NSCLC patients. Moreover, blocking this pathway provides a potential therapy target in lung cancer.