[en] Dry oxidation of spent ion exchange resin is one of the most effective methods to reduce radioactive waste volume and also to make the final waste form more stable. Thermogravimetric measurements were performed using cation exchange resins with or without Fe in either an ionized or unionized form to clarify the effect of metallic impurities on the resin oxidation. The presence of an ionized Fe resulted in a considerable increase in the reaction rate constant, indicating that the Fe functioned as a catalyst. On the other hand, the unionized Fe showed no catalytic activity. Measurement of EPMA revealed that the ionized Fe was distributed uniformly throughout the resin particles, while the unionized one was distributed only on the surface of the resin particle. Catalytic activity increased with ionized Fe concentration up to 0.5 m mol-Fe/g-dry resin, above which the activity tended to decrease. The X-ray diffraction study attributed this to Fe coagulation in the resin particle. Kinetic models for solid-gas reactions were also applied to the resin oxidation to evaluate catalytic activity quantitatively. (author)