A modified sol-gel method was used to fabricate (Pb0.25BaxSr0.75-x)TiO3 (PBST) thin films with x=0.05,0.1,0.15 and 0.2 on Pt/TiO2/SiO2/Si substrate. The structure, surface morphology, dielectric and tunable properties of PBST thin films were investigated as a function of barium content (x). X-ray diffraction and scanning electron microscopy analysis showed that we could get pure PBST perovskite phase and relative fine density thin films with smooth surface. It was found that the crystal lattice constant, grain size, room temperature dielectric constant, dielectric loss and tunability of Ba solutionizing PST thin films increased with the increase in Ba content. For (Pb0.25Ba0.2Sr0.55)TiO3 thin film, it had the highest dielectric constant of 1390 and the largest tunability of 80.6%. The figure of merit parameter reached a maximal value of 28.9 corresponding to the (Pb0.25Ba0.05Sr0.7)TiO3 thin film, whose dielectric constant, dielectric loss and tunability measured at 1 MHz were 627, 0.024 and 69.4%, respectively. (C) 2007 Elsevier B.V. All rights reserved.