The present invention is to provide a method by which, in carrying out a liquid-phase oxidation reaction using a catalyst comprising a tungsten species as an essential component, the catalytic activity performance can be improved or maintained and by which the catalyst component tungsten species can be prevented from being leached into liquid reaction mixtures to thereby control decrease in catalytic activity and make it possible to reuse the catalyst.A method of liquid-phase oxidation reaction using a tungsten species, wherein that, in carrying out said method of liquid-phase oxidation reaction using a catalyst comprising a tungsten species as an essential component, said tungsten species is caused to be supported on a porous support and, further, a third element other than the component elements of said porous support and the tungsten element is caused to coexist in said catalyst.