Abstract: Mesoporous amino-functionalized adsorbents for post-combustion CO2 capture were synthesized by grafting and sol–gel methods. The silsesquioxane obtained by polycondensation of bis[3-(trimethoxysilyl)-propyl]amine without a cross-linker had the highest amount of surface amino groups. Their content was 8.4 times higher than in the grafted material prepared with the same precursor. All obtained materials were tested in CO2 reversible adsorption from a gas stream. The bridged silsesquioxane adsorbent had the adsorption capacity 4.7 times higher than the grafted sample obtained from the same precursor. Porosity study of this material revealed wide pore size distribution with notable fraction of macropores. The nature of adsorbed species was determined from the FTIR spectrum after adsorption. It was found that CO2 formed carbamate and bicarbonate species on the surface.