The tribochemical activation of vanadium pentoxide V2O5 is studied by means of X-ray diffraction, electron microscopy and electron energy-loss spectroscopy. The two-stage process can be described as crushing of large crystals into small ones (macroscopic process) followed by amorphisation and reagglomeration of the fragments (microscopic process). No milling equilibrium state can be found. Energy-loss spectra reveal the reduction of vanadium via oxygen loss. The formation and distribution of V4+ or V3+ species depends on the history of milling.