On the basis of experimental data for carbon dioxide absorption into aqueous nanometer sized colloidal silica solution as a non-Newtonian fluid, a dimensionless correlation for volumetric liquid-side mass transfer coefficient (k(L)a) of CO2 in the flat-stirred vessel was proposed. In addition to ordinary liquid properties and operating parameters such as impeller size and speed in the vessel, Deborah number, which is defined as the product of the characteristic material times of the liquid and agitation speed in the flat-stirred vessel and represents the viscoelastic behavior of non-Newtonian fluid, was used to present unified expressions for k(L)a in Newtonian as well as non-Newtonian liquid. The values of k(L)a in the aqueous colloidal silica solution were reduced due to elasticity of the solution.