The oxidative dehydrogenation of n-butane was investigated over VMgO mixed oxide and pure magnesium ortho- and pyrovanadate catalysts. The formulation containing 30 wt% V2O5 and consisting of the Mg-3(VO4)(2) and MgO crystal phases is more selective than the pure Mg-3(VO4)(2), while the Mg2V2O7 phase is the least selective. The selectivity to butanes and butadiene increases with the reaction temperature and the feed molar ratio of butane/oxygen. Addition of water tends to decrease the conversion of butane and enhances the oxydehydrogenation product selectivity. The relative importance of the primary and secondary paths of the reaction network was analyzed by the method of addition of intermediate products.