Differential heat of absorption of CO2 in aqueous solutions of N,N-diethylethanolamine (DEEA) and activated DEEA solutions up to a total concentration of 2 mol.L-1 was measured as a function of CO2 loading at 313.15 K using a reaction calorimeter. In order to analyze the performance of N-methyl-1,3-propanediamine (MAPA) as an activator, DEEA blended solutions containing 0.05, 0.1 and 0.2 mol.L-1 MAPA were studied. The heat of CO2 absorption in single DEEA solutions was unaffected by changing the DEEA concentration in the range of (0.5-2) mol.L-1. On the other hand, increasing the concentration of MAPA in aqueous amine mixtures of (DEEA + MAPA) raised the heat of absorption. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.