Formation behavior of anodic aluminum oxide (AAO) films was studied when aluminum foils were anodized in hot glycerol electrolyte containing 10 wt.% K2HPO4 in temperatures of 120-200 degrees C. The characteristics of the present anodization including the current density change with time, the effect of applied voltage and electrolyte temperature on anodization behavior, and the morphology and the porous structure resulting from anodization in temperatures of 120-160 degrees C indicated that the present anodization regime is very similar to the conventional one for formation of nanoporous AAO films near room temperatures. Two-step anodization under 50V at 160 degrees C resulted in an AAO film with relatively well-ordered pore channels. Anodization at 180 degrees C, on the other hand, led to formation of an AAO film with a new mesosponge structure that is consisted of nanopores and nanochannels. The mechanism related to the structure transformation is not known at present. (C) 2012 Elsevier Ltd. All rights reserved.