We report the experimental studies of the vibrational spectra ofSrTiO3films grown by pulsed laser deposition. Raman scattering, with and without bias electric field, and Fourier-transform far-infrared ellipsometry between 30 and 700 cm−1have been utilized for investigation of the phonon behavior. These results are discussed in connection with the low-frequency dielectric properties of theSrTiO3films. In the films, the soft mode reveals hardening compared to that in bulk crystals. This observation is in agreement with the Lyddane-Sachs-Teller formalism. The existence of local polar regions is proposed as an important factor determining the dielectric properties of ferroelectric thin films. ©2000 American Institute of Physics.