A new method based on addition of polyethyleneimine (PEI) functionalized HKUST-1 into an aqueous methyldiethanolamine (MDEA) solution for absorption of carbon dioxide is developed. HKUST-1 was synthesized via solvothermal method and functionalized with polyethyleneimine after activating by heating at 120 degrees C for 12 h. Addition of 0.2 wt% of PEI-HKUST-1 to aqueous solution of 40 wt% MDEA at different temperatures (303.15, 313.15, 323.15, 333.15 K) and carbon dioxide pressures up to 2200 kPa, increased the CO2 absorption capacity up to 16%. Absorption capacity was increased with increasing partial pressure of carbon dioxide and decreased with increasing temperature for both solutions. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.