ZnO thin films which were prepared by radio frequency technique with different substrates temperature were investigated optically. The both of first linear optical susceptibility (χ(1)) and third order non-linear optical susceptibility (χ(3)) were determined. Moreover, other important non-liner optical parameters such as non-linear refractive index and non-linear absorption coefficient βc were determined for these studied samples. The electric susceptibility χc and relative permittivity εr for these samples were calculated optically. Finally, important semiconducting parameters such as density of valence band Nv, density of conduction band Nc, free carrier concentration (Nd-Na), position of Fermi level Ef and surface electric field Es were determined for these studied samples.