Abstract: In this paper, the effect of activation procedure in butane-air mixture on the performance of Vanadium-Phosphorus-Oxygen catalysts for oxidation of "butane to maleic anhydride are systematically studied. The catalysts were characterized before and after activation by XRD, IR, TEM, SEM, EPMA and specific surface area determination. Experimental results indicated that activation procedure had an obvious influence on the phase transformation (precursor→ amorphous phase→(VO)2P2O7→β-VOPO4), specific surface area and surface phosphorus/vanadium ration of the catalyst. The morphology of catalysts remained unaltered during activation, but the platelets graduall ybacame smaller. It was shown that vanadyl pyfophosphate ((VO)2P2O7) is the active phase of the catalyst and the catalytic properties are related not only to surface area, but also to the phase composition. Furthermore, a catalyst containing primarily the active phase (VO)2p2O7 was obtained under appropriate activation condition. This catalyst exhibited high activity and good selectivity to maleic anhydride and approached to a steady activity in a short time.