Abstract: A process for the preparation of oxidation catalysts containing vanadium-phosphorus mixed oxides, consisting of: a) contacting a phosphorus compound with a vanadium compound in an organic solvent under conditions allowing the preparation, recovery, drying of said precursor, b) submitting the precursor, prior to calcination, to a treatment by contacting with a stream of dry inert gas containing vapors of an aliphatic anhydride, having from 4 to 8 carbon atoms, preferably acetic anhydride, at a temperature not exceeding 200° C., c) calcinating the precursor under an atmosphere containing air, steam, or inert gas or a mixture of them at a temperature between 350° C. and 550° C. at controlled rate of temperature increase during the time necessary to obtain active catalysts, d) using of said catalysts for the production of maleic anhydride by oxidation of aliphatic hydrocarbons.