Results are presented for the Raman spectra, the far‐infrared reflectivity spectra, and the radio‐frequency dielectric constant of several selected PLZT ceramics. Vibrational modes are assigned by comparing these results with previous Raman and infrared measurements on single‐crystal PbTiO3, and the PZT and PLT mixed ceramic systems. The mode responsible for the temperature variation of the low‐frequency dielectric constant was not observed but is shown to be below 65 cm−1.