A series of mesoporous silica materials, MCM-41, MCM-48, SBA-15, SBA-16, and KIT-6, was synthesized and impregnated with 50 wt% polyethyleneimine (PEI) in methanol to evaluate the performances of the materials in terms of CO 2 adsorption (adsorptiondesorption in 150 min cycle each at 75 Β°C). These PEI-loaded mesoporous silica materials were characterized by XRD, N 2 adsorption isotherm, TGA, and TEM/SEM to monitor their textural properties before and after PEI-impregnation. All the PEI-loaded mesoporous silica samples exhibited reversible CO 2 adsorption-desorption behaviors with >99% recovery. The CO 2 adsorption capacities of the materials were substantially higher than that of pure PEI (79 mg CO 2 /g-adsorbent), and varied in the order of KIT-6 > SBA-16 SBA-15 > MCM-48 > MCM-41. The PEI-loaded mesoporous silica samples also showed faster adsorption kinetics than pure-PEI, and the performance of these materials as a CO 2 adsorbent was influenced primarily by their pore size. KIT-6 with the largest pores in 3D arrangement was impregnated with 50 wt% PEI, and showed the highest CO 2 adsorption capacity (135 mg/g-adsorbent) in the fastest response time. It also exhibited stable adsorption-desorption behavior in three consecutive test cycles in 900 min.