In this paper we report on optical absorbance as characterization technique to determine the electronic nature and, to a certain extend, also the structural properties of sol-gel deposited thin films in the 10 nm to 100 nm thickness range. In particular we have addressed the band structure of the TiO2 layers using band edge optical absorbance measurements; the crystallographic structure (i.e. amorphous, anatase, rutile, and brookite) after heat treatment in wet atmosphere was verified using X-ray diffraction (XRD) and Raman spectroscopy. In the case of structural properties we found that - after heat treatment at 200 degrees C - amorphous structural properties dominate while at higher temperatures (e.g. 500 degrees C) the anatase polytype is dominant. While XRD and Raman spectroscopy fail for 10 nm thin layers, optical absorbance proved to be a valid tool. The latter being of particular interest for the function of TiOx layers in electronic devices like sensors and solar cells. The aim of the paper is to discuss appropriate optical characterization tools for thin sol-gel processed TiO2 films. (c) 2007 Elsevier B.V. All rights reserved.