Three Rh catalysts supported on CeO2 with different specific surface areas and redox properties were prepared and evaluated for their ability to trigger the oxidative reforming of n-butane from ambient temperature (≈300 K). The reference CeO2 catalysts supplied by the Catalyst Society of Japan (JRC-CEO-1, -3, and -4) were used as supports. Temperature-programmed reduction and O2 titration measurements over the reduced catalysts indicated that a high number of surface CeO2 sites that were reducible below 573 K were present on the Rh/CEO-3 catalyst; this catalyst had the largest specific surface area, and it generated sufficient heat by oxidizing CeO2−x [ΔH(298 K)=−368 kJ; x=0.5] after H2 reduction at 773 K. Furthermore, the temperature-programmed reactions revealed that forming fine Rh particles on the high surface area of CEO-3 lowers the autoignition temperature (498 K) of the oxidative reforming of n-butane because the number of exposed Rh sites initiating reactions between n-butane and O2 is large. Thus, the Rh/CEO-3 catalyst could trigger the oxidative reforming of n-butane at ambient temperature after H2 reduction at 773 K owing to the heat generated by the spontaneous oxidation of CeO2−x. In contrast, other catalysts could not trigger the reaction after reduction at the same temperature.