The reduction of SO₂ by CO over supported lanthanum catalysts was studied at the temperature range of 350-550℃, with intial SO₂ concentration of 1,000-10,000 ppm, [CO]/[SO₂] molar ratio of 1.0-3.0 and space velocity of 4,000-12,000 h^-1. We used γ-Al₂O₃, TiO₂, SiO₂ and NaY as the lanthanum carrier. We investigated the reaction activity and selectivity using a differential fixed bed reactor at atmospheric pressure. Results showed that γ-Al₂O₃ is the most effective carrier for the lanthanum catalyst. Over the catalyst prepared by impregnating to γ-Al₂O₃ with 10wt% lanthanum, SO₂ conversion of higher than 95% and COS yield of lower than 3% were obtained at temperatures above 450℃. The optimum [CO]/[SO₂] molar ratio was found to be 2.0. At the [CO]/[SO₂]molar ratios higher than 2.0, the SO₂ conversion was highly increased but the main product was COS. The variation of SO₂ concentrations and space velocity in the experimental range did not affect appreciably on SO₂ conversion and COS yield. X-ray diffraction results revealed that mixtures of La₂O₂S and La₂O₂S₂ was observed after activation, and that the crystal phases were unchanged after reaction.