In order to understand the behavior of COS in the ZnS zone of a packed bed high-temperature desulfurization reactor, the catalytic character of ZnS for the conversion of COS to H2S in the presence of gases which are composed of coal-derived gas was studied. ZnS was active for the catalytic hydrolysis of COS in simulated coal-derived gases; ZnS was also active for the hydrogenation of COS to H2S, but the activity, was considerably lower than that for the hydrolysis of COS. In simulated coal-derived gases, ZnS was also active for the reverse reaction; H2S was converted to COS over ZnS. The water gas shift reaction did not proceed in parallel with hydrolysis of COS over ZnS. From the results of this work, it is suggested that if the contact time of COS with ZnS was sufficient, the equilibrium of the conversion of COS to H2S was controlled by the following reaction : 2COS + H2 + H2O <-- --> 2H2S + CO + CO2.