Abstract: The object of the present invention is to provide a method for preparing a catalyst for producing methacrylic acid by subjecting methacrolein, isobutyl aldehyde or isobutyric acid to gas phase catalytic oxidation with high yield and high selectivity. A method for preparing a catalyst for producing methacrylic acid by subjecting methacrolein, isobutyl aldehyde or isobutyric acid to gas phase catalytic oxidation, the method comprising: (a) a step of blending compounds each containing any one of Mo, V, P, Cu, Cs or NH4 with water to prepare an aqueous solution or dispersion of the compounds (hereinafter referred to, both included, as a slurry); (b) a step of drying the slurry obtained in the step (a) to obtain a dried slurry; (c) a step of calcining the dried slurry obtained in..