The CO2 adsorption performance of MgO in the presence of water vapor is of great importance for CO2 capture and was studied in a fixed bed in this work. With the relative humidity at 50 degrees C increased from 30% to 70%, the CO2 adsorption capacity of MgO increased from 0.82 mol/kg to 3.42 mol/kg correspondingly. The CO2 adsorption capacity could reach as high as 3.54 mol/kg at adsorption temperature of 75 degrees C and a concentration of water vapor of 8.547% v/v. But the time to equilibrium increased due to the restrained CO2 diffusion caused by the condensation of water vapor. Results on cycle experiments implied that condensed water would accelerate the aggregation of MgO particles. It was also found that when the temperature was higher than 100 degrees C, the condensation of water vapor would not happen and the porous structure would keep stable in the cycling adsorption. When the adsorption temperature is between 100 degrees C and 110 degrees C, the degradation of porous structure could be eliminated and the increase of CO2 adsorption capacity could be achieved at the same time. This work indicates that MgO is a promising candidate for CO2 capture from wet flue gas. (C) 2016 Elsevier Ltd. All rights reserved.