In this work, MgO with various porous structures was prepared under different calcination temperatures for carbon dioxide adsorption. The synthesized samples were characterized by X-ray diffractometer, scanning electron microscopy and specific surface area and porosity analyzer. The CO2 adsorption characteristics of MgO were studied by thermo gravimetric analyzer, horizontal attenuated total reflectance Fourier transform infrared spectroscopy and temperature programmed desorption. Experimental results showed that increasing the calcination temperature led to large particles and pore size so that the BET surface area decreased from 101 m2/g to 53 m2/g. Consequently, MgO with large specific surface area synthesized at low calcination temperature yielded high CO2 adsorption capacity. It was also found that chemisorption was the main mechanism in the CO2 adsorption of the synthesized MgO samples and the surface chemistry kept stable under different calcination temperatures. This study suggests that the micro porous structure of MgO can be easily and well controlled by the calcination temperature to attain high CO2 adsorption capacity.