[en] The character of changes of anodic oxides properties (refractive indexes for metal and oxide, the intensity of field in oxide and leakage currents) depending on Ta-Nb alloy composition has been investigated using the methods of ellipsometry and Auger spectroscopy. It has been established that the leakage current changes approximately linearly with composition, but no additivity in other oxide parameters change is found out. Only 10-20% of niobium in an alloy sharply change the values of these parameters and make them close to the parameters of pure Nb