Predicted by the theory, ferromagnetism is expected in Co-doped ZnO. Recently, ferromagnetism above room temperature was reported in thin films as well as in bulk samples made of cobalt-doped zinc oxide. In this study, we report the preparation of ZnO doped with similar to 5% of Co (Zn1-xCoxO, x = 0.05) by electrodeposition. Sample characterization using X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy shows that the dopant is substitutional. Moreover, the magnetic properties of Co-doped ZnO samples electrodeposited as a function of field and temperature exhibit clearly ferromagnetism with Curie temperature above 400 K. (c) 2006 The Electrochemical Society.