We report on the magnetic and structural properties of 2% and 4% Co-doped ZnO diluted magnetic semiconductors prepared by mechanosynthesis. We show that this low-temperature preparation technique does not allow obtaining ferromagnetism in such materials, as already observed in samples prepared by high-temperature techniques. Although X-ray diffraction and UV-Vis spectroscopy indicate that Co ions are well inserted in the ZnO wurtzite structure and that mechanosynthesis is susceptible to generate thermodynamically unstable defects. ferromagnetism observed at 5 and 295 K is systematically attributed to parasitic phases, The pure ZnO:Co phase presents no ferromagnetism in agreement with the high temperature prepared samples. (c) 2006 Elsevier B.V. All rights reserved.