The crystal structure and electrical properties of (Ba0·5Sr0·5)TiO3thin films deposited on various Pt-base electrodes by RF magnetron sputtering, have been investigated. Surface morphology and crystallinity of Pt films for bottom electrode changed with deposition temperature for Pt. The Pt films deposited at 400°C by sputtering have perfectly (111) preferred orientation and dense surface with hillock-free morphology. An 100nm BST film has a dielectric constant of 575 and a leakage current density at 2V of 1·8 × 10−7A/cm2. It is clear that the bottom electrodes are important in determining preferred orientation and electrical properties of BST thin films. With increasing film thickness of BST, the grain size of BST films gradually increased. Dielectric constant of the BST films deposited at 600°C also increased with increasing grain size. It was measured that the dielectric constant decreases from 758 to 348 with the grain size of 82–32nm in the BST films.