A sample of MgO was successfully synthesized using thermal decomposition of hydromagnesite and compared to commercial material. The characterization of materials using XRD, SEM, BET and BJH methods showed that the thermal decomposition way led to rectangular mesoporous microsheets with high specific surface area of 100 m² g⁻¹. This porous magnesium oxide has been shown to be a potential candidate for CO₂ capture at low temperatures range (30 and 50 °C), low pressures of CO₂ (P_CO2=600mbar) and in the presence of water vapor (P_H2O=15mbar). In these conditions, our results show that 11% of MgO was converted to hydrated magnesium carbonate MgCO₃·3H₂O after 8 h of carbonation in a thermobalance and reached 54% after 24 h of carbonation using tube furnace. After carbonation, hydration reaction pore size and surface area have noticeably changed.