A pure and well-crystallized (VO)(2)P2O7 catalyst was oxidized under an oxygen flow at 500 degrees C for different times up to 24 h. These samples were characterized by TGA-DTA, XRD, UV-VIS spectroscopy, and P-31 NMR. Their catalytic performances were compared in the selective oxidation of n-butane to maleic anhydride (MA) as a function of the time of oxidizing pretreatments. The sample oxidized for 1 h displayed an important increase in MA selectivity (from 52 to 84%), whereas the activity remained virtually nonaffected. These results have been discussed in relation with the development of a proper density of selective V-V species associated with the creation of structural disorder in the pyrophosphate lattice.