PbTiO3 thin film with pervoskite-type microstructure was synthesized directly on the α-Al2O3 substrate using a RF-magnetron sputtering system with a composite target. An effective method was developed to get the optical properties from the transmittance spectrum of the sample, and the dependences of refractive index and extinctive coefficient on wavelength were calculated with this method. The band-gap energy of the film was found to be 3.65 eV from the linear fitting of the absorption coefficient to the Tauc plot of (αhν)2 vs hν.