The ZnO thin film doped indium has been fabricated by the sol–gel spin coater technique. The XRD confirmed the pristine ZnO and ZnO:In are polycrystalline phase. The optical constants (n, k) have been determined in terms of two analyses methods, the first was by Kramer kronig relation, and the second was by fitting a spectroscopic ellipsometric (SE) data (w, D) by means of the three-layer optical model. The calculated optical constants in terms of two analyses were comparable and affected by additional In at the expense of ZnO. The optical band gap reduced by the increase of the indium content at the expense of Zn from 3.1 to 2.7 eV. The atomic force microscope (AFM) was used to investigate the surface roughness, which was nearly approached with the surface roughness investigated by SE.