An ammoxidation method in a fluidized-bed reactor, in which, when a starting material to be ammoxidized is ammoxidized by means of vapor-phase catalytic fluidized-bed reaction, the reaction is carried out in a fluidized-bed reactor to which an oxygen-containing gas is fed through feed openings provided at the bottom thereof, and a starting material to be ammoxidized is fed through feed openings provided above the feed openings for the oxygen-containing gas, the distance between the feed openings for the oxygen-containing gas and those for the starting material being from 30 to 250% of the height of a fluidized solid matter in a static state so as to form such a fluidized bed that the density of the fluidized solid matter at the feed openings for the starting material to be ammoxidized is in the range of 50 to 300 kg/m.sup.3 and that the gas velocity is 1 m/s or lower. By this method, the efficiency of contact between catalyst particles and a starting material, and the result of the reaction (the yield of a desired product) are improved.