Different iron oxides, usually used as gold supports, were tested as catalysts for CO oxidation at low temperature. Calcinations of synthesized magnetite at different temperatures, before the activity test, caused its chemical transformations but differences in the activity were not noticeable in all the cases. A sample calcined at 873 K was significantly less active than samples calcined at 473 and 673 K. FTIR measurements in a vacuum showed that the differences in the activity were not caused by the chemical composition but by amount of surface -OH groups. (c) 2006 Elsevier B.V. All rights reserved.