WO3 Nanocrystalline thin films were prepared by Electron Beam Evaporation on cleaned glass substrates. The effect of annealing temperature on the structural, morphological, and optical properties of WO3 thin films has been studied. The single-phase monoclinic structure of the WO3 3 films has been confirmed by x-ray diffraction analysis, all films have homogenous morphology surfaces. The transmission of prepared films was measured in the wavelength range 300-900 nm. WO3 thin films show the indirect band gap ware decreased from about (3.193 eV) before annealing to about (3.061 eV) and (2.952 eV) after annealing.