The promoting effect of alkali nitrates molten salt on the CO2 capture capacity of a commercial MgO was investigated in detail. In particular, the ratio of Li/Na/K nitrates and the loading of the molten salt mixture on the MgO particles were optimized, and the influence of calcination and adsorption temperatures was evaluated. The MgO sample doped with 10 mol % (Li-0.3,Na0.6K0.1)NO3 was demonstrated to possess the highest CO2, uptake (up to 16.8 mmol g(-1)), which is the highest value reported for MgO based adsorbents in the literature. The CO2 adsorption/ desorption cycling stability was studied using both temperature swing adsorption (TSA) and pressure swing adsorption (PSA). The morphology and structure of the optimized adsorbent, 10 mol % (Li0.3Na0.6K0.1)NO3MgO, were characterized thoroughly using XRD, SEM, FTIR, and BET analyses. The thermal stability of doped alkali nitrates was investigated via temperature program desorption and XRD analysis, which indicated that the phase status of the molten salts is crucial for the marked improvement in CO2 capture capacity of MgO.