We study the effect of a rare earth (RE) catalyst on the kinetics of gas carburizing of 08F and 8620 steels. Carburizing was conducted in a sealed-quench furnace employing an endothermic atmosphere with and without RE addition at 900 degreesC for different times. These experimental results show that compared with conventional gas carburizing the incorporation of RE leads to an obvious increase in layer depth and carbon (C) concentration profile under the same carburizing condition. Cerium (Ce) existing in the carburizing atmosphere and diffusing into the surface layer does not change the kinetics law of carburized layer growth. In addition, the calculated results show that the reaction constant and the diffusion coefficient of carbon between the gas-solid interface can also be increased during RE carburizing.