The Co-doped TiO2 nanotube arrays have been synthesized by a sol-gel template method and were characterized by a variety of techniques. The obtained nanotube arrays were identified to be of an anatase structure without any impurity phase. Also, the Co was incorporated in the anatase TiO2 lattice as Co2+ and substituted for the Ti site with no evidence of metallic Co. The ferromagnetic behavior was clearly observed at room temperature in the as-synthesized nanotube arrays, which is related to the oxygen vacancies created by the Co2+ substitution of Ti4+ site in TiO2, not being caused by Co metal. (c) 2006 Elsevier B.V. All rights reserved.