The structural and dielectric properties of anodic oxide films on Nb and Nb-Ti alloys containing 1,3,5,7,10 and 15 at.% Ti were investigated. Anodized Nb-Ti alloys were covered with an anodic oxide film containing amorphous and partly crystalline Nb(2)O(5) and TiO(2), Increase of the Ti content in the alloy resulted in the increase of the anodic oxide film thickness and the amount of TiO(2) in the oxide film, which led to an enhancement of the permittivity and a suppression of the leak current of the anodic oxide film. Therefore, both the capacitance and the leak current of anodized Nb-Ti alloys can be improved by controlling the composition of the alloy. (c) 2008 Elsevier B.V. All rights reserved.