In order to use coke oven gas (COG) as a chemical feedstock and/or city gas, it is necessary to reduce or eliminate various impurities, especially sulfur compounds, found in COG. Catalysts active at around room temperature were explored as a means of removing a sulfur compound, carbonyl sulfide (COS), through catalytic hydrolysis at low temperatures. An alumina impregnated with potassium carbonate was found to show high catalytic activity. COS was hydrolyzed in the low temperature range of 10 and 80 degrees C. The reaction rate was first order with respect to COS and zero order with respect to water. However, the rate decreased rapidly as the water vapor pressure increased in the region over approximately 1.5 kPa at 40 degrees C because the hydrolysis reaction was inhibited by a large amount of water adsorbed on the catalyst. In COG containing large amounts of hydrocarbons and carbon dioxide, the developed catalyst exhibited high long-term activity for COS hydrolysis at between 40 and 50 degrees C under atmospheric pressure.