Carbon dioxide was absorbed into an aqueous nanometer-sized colloidal silica solution in a flat-stirred vessel at 25 ℃ and 101.3 kPa to measure the absorption rate of CO2. The concentrations of silica were in the range of 0-31 wt% and the sizes were 7, 60, and 111 nm. The solution contained monoethanolamine (MEA) of 0-2.0 kmol/m3. The volumetric liquid-side mass transfer coefficient (kLa) of CO2 was correlated with the empirical formula representing the rheological property of silica solution. The use of the aqueous colloidal silica solution resulted in a reduction of the absorption rate of CO2 compared with Newtonian liquid based on the same viscosity of the solution. The chemical absorption rate of CO2 was estimated by film theory using kLa and physicochemical properties of CO2 and MEA.