Thin films of (BaxSrj-x)TiO3 (BST) deposited by RF sputtering have been studied for the application to the capacitor material of dynamic random access memory (DRAM). The effects of film structures on the dielectric constant and the leakage current were investigated. The films deposited at 550–600°C consist of granular grains, and the films deposited above 650°C contain columnar grains. The dielectric constant is related to the grain size in the direction of thickness. The leakage current increases as the film structure changes from granular to columnar. The low leakage current (less than 10−8 A/cm2 at +2 and -2 V) and the small value of equivalent SiO2 thickness (0.9 nm) were attained in the (Ba065Sr035) TiO3 thin films.