Thin films of Ni(OH)x prepared by an alternately dipping deposition (ADD) technique onto ITO substrates present electrochromic efficiencies of 35 cm2/c and optical density variation around 30% on bleaching/coloring cycles in 0.1 M KOH solution. The dependence of the electrochromic performance on the stoichiometry, structure, and morphology of the studied material was investigated by means of variations on those properties induced by heat treatments. The ADD technique also allowed the growth of samples in a powder form that could be analyzed easily by TGA, DSC, and XRD. The results point out that changes in stoichiometry are followed by changes in structure and that the presence of OH radicals in this material is essential for the observation of electrochromic contrast.