The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over Al2O3-supported and zeolite-supported Rh catalysts. The activities of Rh/Al2O3 and Rh/USY (ultrastable Y zeolite) catalysts prepared from Rh(NO3)(3) were higher than those of Rh/ZSM-5 and Rh/ZnO reported in the literature, while the activity of a Rh/Al2O3 catalyst prepared from RhCl3 was suppressed severely in spite of the high H/Rh and CO/Rh values. The catalytic activity of N2O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used.