Strontium-modified lead titanate thin films with composition Pb_1−xSr_xTiO₃ were grown on Pt/Ti/SiO₂/Si substrates using the polymeric precursor method. The structural phase evolution as a function of the Sr contents was studied using micro-Raman scattering, specular reflectance infrared Fourier transform spectroscopy, and x-ray diffraction. The results showed a gradual change from tetragonal to cubic structure, the transition occurring at about x = 0.58. The infrared reflectance spectra showed that the frequency of several peaks decreases as the strontium concentration increases. These features are correlated with a decrease in the tetragonal distortion of the TiO₆ octahedra as the strontium concentration increases.