92%Pb(Mg1/3Nb2/3)O3-8%PbTiO3 (PMNT) thin films have been prepared on Pt/Ti/SiO2/Si substrate with a LaNiO3 (LNO) buffer layer and on sapphire substrate by chemical solution deposition, respectively. X-ray diffraction analysis shows that the PMNT thin films on Pt/Ti/SiO2/Si substrate are almost pure perovskite phase with (110)-preferential orientation. The optical constants (n, k) of the PMNT thin films in the wavelength range of 2.5—12.6μm were obtained by infrared spectroscopic ellipsometry measurement. By fitting the optical transmission spectra of the PMNT thin films on sapphire substrate in the wavelength range of 200—1100nm, the optical constant (n and k) and absorption coefficient (α) were obtained. And that the bandgap energy of the PMNT thin films on sapphire substrate was found to be about 4.03eV.