Lanthanum oxysulphide was found to be an effective catalyst for the reduction of SO2 by CO to elemental sulphur. Over 98% in SO2 conversion and selectivity to elemental sulphur can be achieved under the following conditions : temperature above 500 degrees C, stoichiometric CO/SO2 feed ratio, and a space velocity 21,600 cc g(-1) h(-1). COS in the low ppm level was detected as a by-product similar to our earlier work with perovskite. The catalyst is resistant to oxygen and water vapour. In addition, it was recognised that the lanthanum oxysulphide is bifunctional, i.e., not only is it active in the reduction of SO2 by COS [J.A. Baglio, Ind. Eng. Chem., Prod. Res. Dev., 21 (1982) 38], but also its lattice sulphur atoms are mobile enough to form COS with CO. This suggests that lanthanum oxysulphide functions as a catalyst for the reduction of SO2 by CO via the intermediate COS.