A vanadyl pyrophosphate catalyst for the selective oxidation of n-butane to maleic anhydride (MA) was prepared based on an improved route of the preparation of the catalyst-precursor VOHPO4 . 0.5 H2O in aqueous medium. The precursor is synthesized by conversion of V2O5 with H3PO4 using oxalic acid as reductant and by a controlled procedure of crystallization. After transformation of the precursor into (VO)(2)P2O7 by partial oxidative calcination the catalyst obtained is equilibrated within a few hours using a special conditioning procedure. The catalyst prepared exhibits a high activity and selectivity comparable to that of a catalyst prepared from organic medium.