V2O5-ZrO2 catalysts of different composition were investigated by means of X-ray diffraction, Laser-RAMAN spectroscopy, temperature programmed reduction and catalytic measurements. At low vanadia contents monomeric vanadyl species and polyvanadate species were found. Alkalimetal additives lead to an increase of the V=O bond length in the sequence of nonpromoted < Li < Na < K. The catalytic activity in the oxidative dehydrogenation of propane is connected to the kind of VOx surface species and correlates with the reducibility.