Carbon dioxide was absorbed into an aqueous nanometer sized colloidal silica solution of 0-31 wt% and triethanolamine of 0-2 kmol/m(3) in a flat-stirred vessel with an impeller size of 0.05 m and speed of 50 rpm at 25 degrees C and 101.3 kPa to measure the absorption rate of CO2. The measured rate of CO2 absorption was compared with the values estimated from the model based on the film theory accompanied by chemical reaction. The volumetric liquid-side mass transfer coefficient (k(L)a(L)) of CO2 decreased with increasing silica concentration and was expressed as an empirical correlation formula presenting the relationship between k(L)a(L) and the rheological behavior of the aqueous colloidal silica solution. Reduction of the measured k(L)a(L) was explained by the viscoelastic properties of the aqueous colloidal silica solution.