The (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 (BSTZ) thin films are deposited using radio frequency (RF) magnetron sputtering, then oxygen gas plasma is treated on the surface of BSTZ thin films. The influence of oxygen plasma on the structure of BSTZ thin films is studied using X-ray diffraction patterns and the influence on the electrical characteristics is developed using an Al/BSTZ/Pt/Ti/SiO2/Si capacitor structure. As compared to that of the BSTZ thin films are not subjected to oxygen plasma treatment, experimental results reveal that the leakage current density of the BSTZ thin films in oxygen plasma treatment decreases as much as two orders in magnitude. In addition, the dielectric constants apparently increase and the leakage current density critically decrease as the oxygen-plasma-treated time increases. These results clearly indicate that the electrical characteristics of the BSTZ films are effectively improved using the process of oxygen plasma surface treatment.