To provide a high performance catalyst using composite oxide for a steam reforming reaction of methanol, and a method for the preparation thereof.

A composite oxide catalyst for a steam reforming reaction of methanol which is characterized in that it is prepared by a reduction treatment of a spinel type compound comprising a ternary or higher component composite oxide having a composition represented by AxByOz, wherein A-O bonding force is B-O bonding force, and by forming nanoparticles of A metal inside pores of porous B-O oxide. A method for preparing the composite oxide catalyst which comprises steps of firing an oxide represented by A-O and an oxide represented by B-O to form a composite oxide, and subjecting a spinel type compound comprising the composite oxide to a reduction treatment at a temperature condition in which nanoparticles of A metal are formed inside pores of porous B-O oxide.