An object of the present invention is to provide a method for producing a catalyst for ammoxidation showing a high yield of acrylonitrile and a method for producing acrylonitrile. A step of preparing a catalyst precursor slurry containing a liquid phase and a solid phase, a step of drying the catalyst precursor slurry to obtain dry particles, and a step of firing the dried particles to obtain a catalyst for ammoxidation, Preparation of a catalyst for ammoxidation in which an aggregate containing a metal and a carrier is contained in a solid phase, the particle diameter of the primary metal particles constituting the aggregate is 1 μm or less, and the average particle diameter of the metal primary particles is 40 nm or more and 200 nm or less Way.