Passivated and nonpassivated tungsten carbide (WC) powders were prepared by a temperature-programmed reaction and used as catalysts in the hydrazine decomposition reaction. All catalysts were active at 313 K. The only products of reaction were nitrogen and ammonia, suggesting that the reaction route and the rate-determining step were not modified by adsorbed oxygen. Surface oxygen atoms reacted with hydrazine, resulting in a larger decrease in the rate of reaction for the passivated solids. Excess carbon on the surface of the carbide inhibited the decomposition of hydrazine and resulted in a decrease of ca. 48% in the specific surface area of the tungsten carbide. The excess carbon may be removed in flowing hydrogen at 1000 K. When compared to commercial Ir catalyst (Shell 405), WC is less active in the hydrazine decomposition reaction.