An object of the present invention is to provide a method for, when stopping an ammoxidation reaction of propane, stopping the ammoxidation reaction safely and quickly, without causing a deterioration in catalytic activity or acrylonitrile yield. The method for stopping an ammoxidation reaction includes a supply stopping step of stopping a supply of propane, an oxygen-containing gas, and ammonia to a reactor where an ammoxidation reaction of propane is being carried out using a catalyst, and a reaction stopping step of supplying an inert gas to the reactor in an amount 10 to 300 times the catalyst volume per hour until the catalyst temperature reaches 380° C. or less, wherein after the supply stopping step, a time required until the catalyst temperature decreases to 360° C. or less is within 10 hours.