_{​Abstract} 

 Stoichiometric Ti_1−xCo_xO₂ and oxygen-deficient Ti_1−xCo_xO_2−δ thin films were grown on Si (001) by plasma-enhanced metal-organic chemical vapor deposition and their microstructures and ferromagnetic properties were investigated. The stoichiometric film grown at 430 °C showed no discernable Co metal clustering or measurable coercive field. In contrast, oxygen-deficient films fabricated without supplying O₂ contained significant Co clusters of ~10–20 nm, which appeared to be the major reason for the observed room-temperature ferromagnetism. With increasing oxygen vacancies of the films, the coercive field and saturation magnetization values increased to ~460 Oe and ~27 emu/cm³ (1.55μB/Co atom) approached that for bulk cobalt, respectively.