The present invention relates to a method for preparing a heteropolyacid catalyst and method for preparing methacrylic acid using thereof. More particularly, the present invention relates to a method for preparing heteropolyacid catalyst, which is produced by the recrystallization of a heteropolyacid and/or its salt dissolved in a basic organic solvent and heat-treatment, and further to a method for preparing metachrylic acid using thereof, wherein the use of the heteropolyacid catalyst increases the activity of oxidation reaction induced by the modified electronic properties of heteropolyanions and provides high efficiency production of methacrylic acid from methacrolein, since the basic property of solvent inhibits peculiar acidic property of heteropolyacid.