In this study, the mechanical properties, such as the modulus, hardness, of anodic aluminum oxide (AAO) structures are measured using the nano-indentation method. Relationship between the mechanical properties and the porosity change is also investigated. Results show that the indentation modulus and hardness of the AAO structure decreases monotically as the hole's size increases. Additionally, we try to evaluate the residual stress that is generated during the anodization process. We find out that there exists residual tensile stress in the specimen structures. (c) 2006 Elsevier B.V. All rights reserved.