We report on the structural, magnetic, optical and transport properties of As-doped Zn0.9Co0.1O thin films. X-ray diffraction indicates highly (0001) textured samples free of secondary phases. Transmission UV-Vis spectroscopy shows that Co is in the +2 oxidation state and substitute for the Zn2+ ions of the ZnO matrix. ZnCoO was doped with 0.5% As which lead to n-type doping. Before and after As-implantation, the films remain ferromagnetic up to 350 K and the magnetization is unchanged. Surprisingly, there is no real influence of the doping process on the exchange interaction mediated by itinerant carriers between magnetic ions. (c) 2006 Elsevier B.V. All rights reserved.