Abstract: This paper deals with the macrokinetics of water gas shift reaction on commercial iron oxide catalysts. In an internal recycle gradientless reactor, type B106 and B109 shift catalysts of commercial size and cylindrical in shape, have been studied under atmospheric pressure. Reaction conditions were: temperature 350° to 480℃, molar ratio of steam to carbon monoxide 2 to 11, dry gas space velocity 150 to 1500ml/(h. g). Experimental results showed that the macrokinetic equations for both catalysts can be expressed by the common formula: where pco, pH2o> pco2 and pH2 are the partial pressures of carbon monoxide, steam, carbon dioxide and hydrogen, respectively, KP the equilibrium constant of water gas shift reaction, k* the apparent rate constant. This equation can be used in the simulation of commercial shift converters. The apparent activation energy of B106 catalyst is 14,570 cal/mol and that of B109 catalyst, 16,200 cal/mol. They are approximately one half the corresponding intrinsic activation energy values, suggesting that the water gas shift reaction process is severely limited by intraparticle diffusion on the other hand, the effectiveness factors for both catalysts, as calculated by use of the experimental results and the intrinsic rates indicate that the apparent activity is much lower than the intrinsic activity, hence pointing out the importance of improving the pore structure and geometry of commercial shift catalysts.