Amorphous and partially crystalline WO3 thin films were prepared by reactive dual magnetron sputtering and successively implanted by erbium ions with a fluence in the range from 7.7 ?? 1014 to 5 ?? 1015 ions/cm2. The electrical and optical properties were studied as a function of the film deposition parameters and the ion fluence. Ion implantation caused a strong decrease of the resistivity, a moderate decrease of the index of refraction and a moderate increase of the extinction coefficient in the visible and near infrared, while the optical band gap remained almost unchanged. These effects could be largely ascribed to ion-induced oxygen deficiency. When annealed in air, the already low resistivities of the implanted samples decreased further up to 70??C, whereas oxidation, and hence a strong increase of the resistivity, was observed at higher annealing temperatures