Transparent thin films of strontium titanate (SrTiO3) were formed on the substrate of quartz glass plate by RF magnetron sputtering with changing the substrate temperatures during the sputtering from 100 to 700 degrees C. The particle size and the lattice constant of the cubic-SrTiO3 crystallites composing the film were exhibited to be changed from 13 to 48 nm and from 4.02 to 3.96 angstrom, respectively, by the change of the substrate temperatures from 400 to 700 degrees C. The UV absorption edges of the transparent film samples shifted to longer wavelength with the increase of the particle size and the decrease of the lattice constant of the nano-crystalline SrTiO3.