Atomic force and high resolution scanning tunneling analyses were carried out onnanostructured WO3 films. It turned out that the band gap measured by scanning tunnelingspectroscopy at surface is lower than the band gap reported in the literature. This effect isattributed to the high density of surface states in this material, which allows tunneling intothese states. Such a high density of surface states pins the Fermi level resulting in modestsurface activity at room temperature. Photo activation of WO3 results in unpinning of theFermi level and thereby in higher chemical activity at surface.