The deactivation rate equation for a commercial Cu/ZnO water-gas shift catalyst was derived on the basis of a high-order power-law equation for sintering rate. The parameters for the equation were then calculated from experimental data obtained over a short period during which the deactivation conditions were severe (250-350 degrees C). The values calculated from an 11th-order deactivation rate equation were in good agreement with the experimental values over a long period (1000 h) under practical conditions (200 degrees C).