The dispersion of the refractive indices for the epitaxialPb1−xLaxTiO3thin films withx=0.28 and 0.23 grown on the MgO (100) andAl2O3(0001) substrates, respectively, has been investigated. The refractive indices in the wavelength range of 435–1523 nm were measured by a prism coupling method. At a wavelength range of 632.8 nm, the refractive index of a PLT film grown with (100) orientation was determined to be 2.609. The transmission spectrum was used as an additional measurement for the dispersion of the refractive index and showed a good agreement with the prism coupling measurements. The dispersion of refractive index fits well to a single-term Sellmeier relation. ©1997 American Institute of Physics.