W-TiO2 (W, tungsten) dual-layer thin films are deposited by RF magnetron sputtering onto glass substrates and annealed at 150oC~400oC for 4hrs. The crystal structure, morphology, and trans- mittance of annealed W-TiO2 dual-layer thin films are investigated by X-ray diffraction, FESEM, and UV-Vis spectrometer, respectively. The annealing temperatures have large effect on the properties of W-TiO2 dual-layer thin films. The band gap energy values of W-TiO2 dual-layer thin films are evaluated from (h)1/2 versus energy plots. The energy gap for un-annealed W-TiO2 dual-layer thin film is 3.16 eV. As the annealing temperature increases from 150oC to 400oC, the energy gap decreases from 3.16 eV to 3.10 eV.