Abstarct: In this experimental thesis the morphological, structural, optical and electrochromic properties of nanostructured nickel oxide (NiO) thin films, which have been grown by spray pyrolysis and hydrothermal methods, have been studied. Synthesized samples were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV-Vis spectroscopy, photoluminescence spectroscopy (PL) and cyclic voltammetry (CV) techniques. Effects of using two different nickel salts as precursors, different solution concentration and different concentrations of Cu as dopant were studied for the growth of NiO thin films using spray pyrolysis. XRD patterns show the formation of cubic crystal structure for NiO samples prepared using two different nickel salts. Also, XRD pattern analysis of NiO thin films deposited using different solution concentrations exhibits growth of hexagonal phase. The calculated band gap value decreased from 3.23 to 3.18 eV with increasing the solution concentration. The FESEM images were also revealed that the grain size increased from 16 to 23 nm, in this case. XRD pattern analysis of Cu-doped NiO thin films indicated the formation of hexagonal crystal structure. In this case, with increasing the cupper concentration, the calculated band gap decreased from 3.62 to 2.84 eV and grain sizes were decreased from 18 to 9 nm according to FESEM image analysis. The FESEM images of undoped nickel oxide indicated agglomeration of particles. However, Cu doped NiO thin films have found to exhibit fully covered surface morphology with densely packed grains. As an affecting parameter, the effect of hydrothermal process time was investigated for NiO samples prepared by this method. FESEM images indicate the formation of spheres with the mean diameter of about 1 µm which have been covered with interconnected nanofibers of about 15 - 40 nm in diameter. XRD pattern analysis of these samples has exhibited the formation of hexagonal phase. Also, samples have been grown by hydrothermal method showed electrochromic properties. Transmittance and photoluminescence spectra of samples recorded and analyzed.