Relaxor ferroelectric 0.74Pb (Mg1/3 Nb2/3) O3-0.26PbTiO3 thin films were prepared on LaNiO3-buffered silicon substrates by radio-frequency magnetron sputtering. The effect of deposition temperature on films' microstructures and optical properties was investigated. The sample deposited at 500 oC exhibits not only a pure perovskite phase, highly (110)-preferred orientation, and dense and crack-free morphology, but also the largest average remnant polarization of 17.2 μC/cm2 among all investigated films. With Cauchy model the refractive indices and extinction coefficients for these specimens have been obtained by fitting experimental reflectance spectra. At a wavelength of 633 nm, the value of refractive index 2.41 was obtained for the thin films deposited at 500 oC. In addition, optical band gaps of the films are in the range of 2.97-3.22 eV. A preliminary discussion has been carried out on the difference in the optical properties of these films.