Abstract The optical and structural properties of sol–gel spin-coated WO 3 and Vanadium-doped WO 3 thin films were investigated. These films have been produced by a sol–gel technique. The refractive index, extinction coefficient and optical band gap of the films have been calculated with respect to the number of coating layers. The surface morphology was analyzed by atomic force microscopy (AFM). Optical constants of WO 3- and V-doped tungsten oxides were determined by using spectrophotometric transmissivity in the UV-visible region.