Four different types of amine-attached MCM-48 silicas were prepared and investigated for CO2 separation from N-2. Monomeric and polymeric hindered and unhindered amines were attached to the pore surface of the MCM-48 silica and characterized with respect to their CO2 sorption properties. The pore structures and amino group content in these modified silicas were investigated by XRD, FT-IR, TGA, N-2 adsorption/desorption at 77 K and CHN/Si analysis, which confirmed that in all cases the amino groups were attached to the pore surface of MCM-48 at 1.5-5.2 mmol/g. The N-2 adsorption/desorption analysis showed a considerable decrease of the pore volume and surface area for the MCM-48 silica containing a polymeric amine (e.g., polyethyleneimine). The CO2 adsorption rates and capacities of the amine-attached MCM-48 samples were studied employing a sorption microbalance. The results obtained indicated that in addition to the concentration of surface-attached amino groups, specific interactions between CO2 and the surface amino groups, and the resultant pore structure after amine group attachment have a significant impact on CO2 adsorption properties of these promising adsorbent materials.