Cr2O3 films 1425 Angstrom thick deposited by reactive r.f. magnetron spluttering onto polycrystalline tantalum substrates were annealed in ultrahigh vacuum between 670 degrees C and 750 degrees C. The temperature induced compositional changes were determined by Auger electron spectroscopy (AES) sputter depth profiling without breaking the vacuum. In comparison with an unheated Cr2O3/Ta couple the annealing procedure leads to a homogeneous reduction of the oxygen content in the Cr2O3 film and an enrichment of chromium in the near-surface region. Based on the concentration depth profiles derived from the AES sputter profiles, the mechanism of oxide dissolution ii discussed in detail. It is described by a first-order reaction for which the temperature dependent rate constants have been determined, For the respective activation energy a value of 5.3 eV uas found.