Abstract: Acrylonitrile is prepared by a process which comprises the ammoxidation of propylene with ammonia and molecular oxygen or a gas containing molecular oxygen at from 300.degree. to 600.degree. C. in the presence of a metal oxide catalyst which contains tellurium and one or more of the metals iron, molybdenum and antimony, in a fluidized bed, with regeneration of the catalyst during the reaction by the addition of oxidic tellurium compounds or tellurium compounds which form oxidic tellurium compounds under the reaction conditions, in dissolved or suspended form.