Objective: Chronic Obstructive Pulmonary Disease (COPD) is a common, preventable, curable disease characterized by persistent airflow limitation, respiratory symptoms due to airway and/or alveolar abnormalities caused by severe exposure to harmful particles, gases. During the endobronchial coil treatment (EBCT) process, the volume of the lung parenchyma is reduced by shrinking the elastic recoil. Although there are studies showing worsening of hemorheological parameters in COPD exacerbations, no study investigated whether hemorheological parameters are improved after coil. The aim of this study was to assess the effects of coil therapy on erythrocyte deformability, whole blood viscosity (WBV) measured at autologous, standard (40%) hematocrit and plasma viscosity (PV) in COPD patients. Material and methods: Venous blood samples were taken once from the healthy control group (n=17) and before and 1 month after the treatment from the COPD patients who had been indicated for coil according to GOLD guidelines (n=20). To assess erythrocyte deformability, shear-dependent erythrocyte elongation was measured at 0.3-3.0 Pa by an ektacytometer (LORCA), while WBV, PV were measured using a rotational viscometer. Results: Erythrocyte deformability measured at shear stresses between 0.3-5.33 Pa were found to be higher following treatment compared to pre-coil values. EBCT did not have a statistically significant effect on WBV measured at autologous, 40% hematocrit, PV and oxidative stress indices. Conclusion: Increased erythrocyte deformability determined following EBCT at the shear stresses observed at the pulmonary level is a favourable finding, showing that the procedure may positively affect the hemodynamics of COPD patients as well as causing clinical improvement.