Nickel oxide films have been prepared by electrochemical deposition on a conducting substrate such as Au or ITO from a basic solution with nickel sulfate and an amino acid. The NiO films thus prepared exhibit typical p-type semiconductor and electrochromic properties. From a Mott-Schottky plot, the flatband potential, V F B and the acceptor density, N A are determined as 0.47 V versus Ag|AgCl (at pH 7.0) and 1.8x10 2 1 cm - 3 , respectively. The optical band gap, E g obtained from measurement of the absorption coefficient of the NiO at a particular photon energy is estimated as 3.31 eV. The absorption spectrum of a NiO|ITO electrode exhibits a maximum at a wavelength of 460 nm in the potential region above +0.4 V. The colors of the nickel oxide are dark blue and transparent in the potential regions above and below this potential, respectively.