Method for producing oxide catalyst and method for producing unsaturated nitrile

A method for producing an oxide catalyst according to the present invention is a method for producing an oxide catalyst containing Mo, V, Sb, and Nb, the method including:a raw material preparation step of obtaining an aqueous mixed liquid containing Mo, V, Sb, and Nb;an aging step of subjecting the aqueous mixed liquid to aging at more than 30° C.;a drying step of drying the aqueous mixed liquid, thereby obtaining a dried powder; anda calcination step of calcining the dried powder, thereby obtaining the oxide catalyst,wherein, in the raw material preparation step and/or the aging step, precipitation of Nb is facilitated by performing at least one operation selected from the group consisting of the following (I) to (III):(I) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein ammonia is added to at least one of the MoVSb raw material liquid, the Nb raw material liquid, and the aqueous mixed liquid such that a molar ratio in terms of NH3/Nb in the aqueous mixed liquid is adjusted to be 0.7 or more, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50° C.;(II) in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 65° C.; and(III) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein a molar ratio in terms of H2O2/Nb in the Nb raw material liquid is adjusted to less than 0.2, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50° C.