Thin films of Ni oxide, a promising anodic electrochromic material, were deposited by reactive radio frequency (rf) sputtering at 40, 60, and 100 W, and their electrochemical and electrochromic properties were examined using neutral KCl electrolytes. Higher charge capacity and higher optical modulation were obtained for a Ni oxide film deposited at low sputtering power and low deposition rate. Electrochromic coloration efficiencies of similar to 30 cm(2)/C were obtained for all the Ni oxide films in KCl regardless of rf power value. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2137471] All rights reserved.