Single-phase iron-substituted nanocrystalline ruthenium dioxide with composition Ru0.98Fe0.02O2-y and Ru0.70Fe0.30O2-y of rutile structure was prepared. The electrocatalytic behavior of the prepared materials was tested with respect to oxygen evolution reaction and chlorine evolution reaction (CER) The substitution with iron leads to a slight increase of the material's activity toward oxygen evolution. The selectivity of iron-doped materials in parallel oxygen and chlorine evolution is affected by oxygen content in the electrolyte solution. The CER is preferred in oxygen-free solutions; in oxygen-saturated solutions oxygen evolution is enhanced. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.2978963] All rights reserved.