The present invention relates generally to catalysts comprising ruthenium oxide and to processes for catalyzing the oxidation and conversion of sulfur dioxide (SO.sub.2) to sulfur trioxide (SO.sub.3) using such catalysts. SO.sub.2 at low concentrations in process gas streams can be effectively oxidized to SO.sub.3 at relatively low temperatures using the ruthenium oxide catalysts of the present invention. In one application, the ruthenium oxide catalysts are used in the final contact stage for conversion of SO.sub.2 to SO.sub.3 in multiple stage catalytic converters used in sulfuric acid manufacture.