Background: Chronic obstructive pulmonary disease (COPD) is characterized by progressive loss of lung function and local and systemic inflammation, in which CD8(+) T-cells are believed to play a key role. Activated CD8(+) T-cells differentiate into distinct subpopulations, including interferon- (IFN-)-producing Tc1 and interleukin (IL)-17-producing Tc17 cells. Recent evidence indicates that Tc17 cells exhibit considerable plasticity and may convert into IL-17/IFN--double producing (Tc17/IFN-) cells when driven by inflammatory conditions. The aim of this study was to investigate the Tc17/IFN- subpopulation in peripheral blood of patients with COPD and to evaluate their potential roles in this disease. Methods: Peripheral blood samples were collected from 15 never-smokers, 23 smokers with normal lung function, and 25 patients with COPD (Global Initiative for Chronic Obstructive Lung Disease 2u4). Proportions of the IL-17/IFN--double expressing subpopulation were assessed using flow cytometry. Plasma concentrations of cytokines favoring Tc17/IFN- differentiation were measured by enzyme-linked immunosorbent assay. Results: Patients with COPD had higher proportions of Tc17 cells and Tc17/IFN- cells in the peripheral blood than smokers and never-smokers. The plasticity of Tc17 cells was higher than that of Th17 cells. The percentages of Tc17 cells and Tc17/IFN- cells showed negative correlations with forced expiratory volume in 1 s % predicted value (r = 0.418, P = 0.03; r = 0.596, P = 0.002, respectively). The plasma concentrations of IL-6, transforming growth factor-1, and IL-12 were significantly higher in patients with COPD compared with smokers and never-smokers. Conclusions: Peripheral Tc17 cells are increased and more likely to convert to Tc17/IFN- cells in COPD, suggesting that Tc17 cell plasticity may be involved in persistent inflammation of the disease.