The absorption rate (RA) of carbon dioxide was measured into an aqueous nanometer sized colloidal silica solution of 0-31 wt% and N-methyldiethanolamine of 0-2 kmol/m3 in a flat-stirred vessel for the various sizes and speeds of at 25 oC and 0.101 MPa to obtain the volumetric liquid-side mass transfer coefficient (kLa) of CO2. The film theory accompanied by chemical reaction between CO2 and N-methyldiethanolamine was used to estimate the theoretical value of absorption rate of CO2. An empirical correlation formula containing the relationship between kLa and rheological property of the aqueous colloidal silica solution was presented. The value of RA in the aqueous colloidal silica solution was decreased by the reduction of kLa due to elasticity of the solution.