A series of potassium-doped barium strontium titanate ((Ba0.5Sr0.5)(1-x)KxTiO3) targets with dopant concentration (x) from 0 to 12.5 mol% were synthesized by solid state reaction and the corresponding thin films were fabricated on (111) Pt/Ti/SiO2/Si substrate by using pulsed laser deposition. The doping of K shows strong influences on structural, dielectric and tunable characteristics. Surface roughness of the films decreases with the doping of K up to 7.5 mol% and then increases with further increase of K, whereas the grain size is found to be minimum at 7.5% K. The maximum values of tunability and figure of merit obtained for the optimum 7.5 mol% K-doped thin films are 77% and 65 at an applied field of 400 kV/cm at 100 kHz, respectively, which corresponds to significant improvements compared to the reported results processed by sol-gel or sputtering. The relaxation of crystalline strain inside the grains, and smoother surface with smaller grains are assumed to be responsible for the improved tunability and lower dielectric loss. (C) 2012 Elsevier B. V. All rights reserved.