Abstract: The present invention relates to a porous carrier for steam-reforming catalysts which is composed of a composite oxide containing at least aluminum and magnesium, and has a BET specific surface area of 10 to 300 m2/g, an average pore diameter of not more than 300 ? and a pore volume of not less than 0.1 cm3/g. The catalyst obtained by supporting an active metal thereon, can be suitably used as a catalyst for steam-reforming a hydrocarbon raw material having a total sulfur content of not more than 50 ppm. The present invention provide a carrier which can be industrially mass-produced and can exhibit an excellent sulfur-poisoning resistance. Further, the catalyst using the porous carrier is very useful for producing a mixed gas of a C1 component and hydrogen by subjecting a sulfur-containing hydrocarbon to a steam-reforming reaction.