Disclosed is a process for preparing a stable PROX reaction catalyst, comprising the steps of (a) preparing a catalyst platinum supported on alumina; (b) calcinating the catalyst from step (a) at 300.about.600.degree. C. for 2.about.4 hours; (c) contacting the catalyst obtained from step (b) with hydrogen at 300.degree. C..about.600.degree. C. for 2.about.4 hours to reduce the catalyst; and (d) dropping the temperature in the reduced catalyst from step (c) to less than 100.degree. C. and then contacting the catalyst with a predetermined solvent and/or gas while elevating the temperature to 300.degree. C. 600.degree. C. The catalyst has Pt--Al arrangement, the content of Pt being 0.5.about.7% by weight and has an overall shape of an oval.