Cerium (Ce)-doped barium strontium titanate (Ba0.6Sr0.4TiO3, BST) films and undoped BST films have been prepared by an improved Sol-gel method. The surface structures have been studied by X-ray photoelectron spectroscopy (XPS). The result reveals that the surface structures are composed of perovskited structure and non-perovskited structure, and the Ce doping significantly reduces the non-perovskited structure. It is by scanning electron microscope and atomic force microscope shown that the Ce-doped BST films are smooth and compact without crack or shrinkage cavity, which are associated with the formation of the non-perovskited structure. The voltage-capacitance curves demonstrate that the Ce-doped BST films have significant improvement in dielectric properties with a tunability of more than 60.8% at 40 voltage, and a dielectric loss (tand) of 0.0265 at zero bias. The improved mechanism of Ce doping is discussed