The electrochemical behaviour of hafnium oxide was investigated in the potential range 0-150 V, in the following electrolytes : H2SO4, H3PO4, NaOH and HNO3. After film growth, AC impedance measurements were performed in the frequency range 0.1 Hz-100 KHz. The impedance spectra of the oxides showed a multilayer structure as the oxide thickness increased, due to anion incorporation From the electrolyte and the corrosion process enhanced by anodic breakdown at high final formation potentials. Anodic breakdown was also investigated. An electric field strength increase with thickness was observed, which could be associated to changes from amorphous to crystalline oxide structure. This fact could produce internal stresses during the oxide growth resulting in an anodic fracture which can be correlated, in turn, with dielectric constant changes.