We report on the structural, magnetic, optical and transport properties of As-doped Zn0.9Co0.1O thin films. X-ray diffraction indicates highly (0 0 0 1) 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. © 2006 Elsevier B.V. All rights reserved.