Sulfation reaction kinetics of CuO/SiO₂-Al₂O₃ sorbent with SiO₂ gas have been determined with the variations of particle size, gas flow rate, SiO₂ concentration and reaction temperature in a thermo-gravimetirc analyzer(TGA). Reactivity of SiO2-A1203 support with SOa gas is found to be negligibly small during the suuation reaction. The order of sulfation reaction with respect to the CuO/SiO₂-Al₂O₃ sorbent is first order and the reaction rate decreases with increasing the particle size (d^p) due to the increase of the diffusion resistance. Sulfation conversion of the sorbent (d^p=0.1 mm) follows the uniform reaction model and the activation energy is found to be 43.8 kJ/mol. When the particle size increases above 0.3 mm, the overall reaction is controlled by the diffusion of SO₂ through the product layer, and the activation energy of the effective diffusivity is 60 kJ/mol.