The mechanochemical treatment of the V-P-O catalysts caused a substantial increase of both the catalytic activity in n-butane oxidation and the selectivity towards maleic anhydride. It was accompanied by a relative growth of the contribution of vanadyl plane (001) of VOHPO4 . 0.5H(2)O which transforms into the topologically similar (100) plane of (VO)(2)P2O7. The mechanochemical treatment of the V-P-O catalysts containing bismuth changes the sample morphology, favouring the formation of the vanadyl plane and provoking surface chemical reaction. The data obtained for V-P-O/BiPO4 and V-P-O/Bi2O3 samples demonstrate that mechanochemistry is a new promising method for the introduction of promoting additives into the basic V-P-O composition.