Based on the analysis of the precise current-time data and observation of the morphology by scanning electron microscopy, a layer-by-layer growth model of anodic TiO2 nanotube (TNT) arrays was presented. Many phenomena appeared during the anodization and can be reasonably explained by this model, such as the first sharp slope of current in initial period, current fluctuation, occurring of ridges in adjacent tubes, and the rings broken off from the tube mouths. Furthermore, key factors which determine the morphology of TNT are discussed and it would be helpful for the design of nanoarchitectures in related material systems. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3514690] All rights reserved.