(Pb1-xSrx)TiO3 (PST) (0 less than or equal tox less than or equal to0.7) thin films on Pt/Ti/SiO2/Si(100) substrate were prepared by the modified sol-gel process and their characteristics were investigated as a function of strontium content (x). A stable PST sol was obtained by mixing lead and strontium acetates dissolved in deionized water and ethylene glycol and a titanium alkoxide modified by chelating acetylacetone in 2-methoxyethanol, The multi-layer annealing at 700 degreesC was adopted to prepare the 4000 degrees PST thin films with perovskite phase and dense microstructure. With increasing x, the tetragonality (c/a) was slightly decreased and approached to cubic phase above x congruent to 0.5 within XRD detection limit. The dielectric constant at room temperature abnormally increased and showed the maximum one (epsilon (r) = 1377, tan(8) = 0.037 at 1 kHz) for the Pb0.5Sr0.5TiO3 thin film. Also strontium substitution suppressed the leakage current density of the films effectively. These properties can be explained in terms of variations of phase transition boundary (tetragonal to cubic), resulting from the substitution of nonvolatile strontium into lead site of PbTiO3 structure.