This paperwas to investigate the effect of carbonation curing on the compressive strength and microstructure of mortarscomprised of reactive MgO, CaO, fly ashand cement. The results show that carbonation curing increases the compressive strengths ofmortars. The increase of temperature or carbonation curing time increases the compressive strengths of mortars. The treatment ofCO2decreases the pH value, enhances the microstructures densification and decreasesthe amount of relatively coarse pores and totalpore volume due to the formation of calcite (CaCO3) andmagnesium calcite (CaxMg1-xCO3).