The reoxidability of vanadyl pyrophosphate is studied by thermal analysis and by temporal analysis of product (TAP). The samples differ by surface area, oxidation state of vanadium, crystallite size, and degree of crystallinity. The morphology ranges from platy to prismatic and the microstructure from mosaic crystals exhibiting {100} faces to bulky crystals. The reactivity of these samples during oxidation as well as their catalytic reactivity studied in flow reactor is accounted for by the microstructure. The highest reoxidation capability and the best catalytic properties in oxidation of n-butane to maleic anhydride are obtained with mosaic crystals.