Abstract: "Radio frequency magnetron sputtering technique is used to deposit Ba0:65Sr0:35TiO3 (BST) thin films on fused quartz substrates. In order to prepare the high quality BST thin films, the crystallization and microstructure of the films were characterized by X-ray diffraction, field emission scanning electron microscopy and atom force microstructure. The more intense characteristic diffraction peaks and better crystallization can be observed in BST thin films deposited at 600 oC and subsequently annealed at 700 oC. The refractive index of the films is determined from the measured transmission spectra. The dependences of the refractive index on the deposition parameters of BST thin films are different. The refractive index of the films increases with the substrate temperature. At lower sputtering pressure, the refractive index increases from 1.797 to 2.179 with the pressure increase. However, when the pressure increases up to 3.9 Pa, the refractive index instead reduces to 1.860. The oxygen to argon ratio also plays an important effect on the refractive index of the films. It has been found that the refractive index increases with the ratio of oxygen to argon increasing. The refractive index of BST thin films is strongly dependent on the annealing temperature, which also increases as the annealing temperature ascends. In one word, the refractive index of BST thin films is finally affected by the films microstructure and texture."