Nanostructured ZnO network films have been fabricated on Al2O3 substrates by the combination of chemical bath deposition and thermal decomposition process. Layered basic zinc nitrate (LBZN) network films were deposited on the Al2O3 substrates with LBZN crystal seeds in methanol solution of zinc nitrate hexahydrate and hexamethylenetetramine. The LBZN precursor films were then transformed into nanostructured ZnO films by heating at 260 degrees C in air. During the thermal decomposition process abnormal exothermic heat effect was observed at 200-210 degrees C and CH3 groups were found in the as-deposited films. We propose that methanol molecules are integrated in the LBZN films forming LBZN-CH3OH complex and that the heat effect comes from the exothermic release of the methanol. (C) 2008 Elsevier B.V. All rights reserved.