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-FB and the acceptor density, N-A are determined as 0.47 V versus Ag\AgCl (at pH 7.0) and 1.8 x 10(21) 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. (C) 2004 Elsevier B.V. All rights reserved.