Anatase Ti1-xCoxO2 thin films onto SiO2/Si substrates at 400degreesC using liquid-delivery metallorganic chemical vapor deposition (MOCVD) were successfully prepared and the ferromagnetic properties investigated through microstructural analysis by transmission electron microscopy and high-resolution scanning Auger microscopy as a function of Co-doping concentration. Ferromagnetic behaviors of polycrystalline films were observed at room temperature and the magnetic and structural properties depend critically on the Co distribution, which varies widely with Co-doping concentration. Annealed Ti1-xCoxO2 thin films with x less than or equal to 0.05 showed a homogeneous structure without any clusters, and pure ferromagnetic properties of thin films are attributed only to the Ti1-xCoxO2 phases. In the case of thin films above x = 0.05,10-150 nm Co-rich Co1-xTix clusters are formed in homogeneous Ti1-xCoxO2 phases. The solid solubility of Co was approximately 5 atom % in MOCVD-Ti1-xCoxO2 polycrystalline thin films. Co1-xTix clusters with a c axis preferred orientation decrease the value of H-c (coercive field) and increase the saturation magnetic field. The polycrystalline anatase Ti1-xCoxO2 thin films prepared by liquid-delivery MOCVD have an advantage for high-density device application in ferromagnetic semiconductor fields. (C) 2004 The Electrochemical Society.