The study of magnetic multilayers consisting of electrodeposited Co layers is gaining significant importance for the application in the field of magnetic recording. However, there are been few studies on the properties of electrodeposited Co thin films. in this paper, the relation between morphology, crystallographic structure and magnetic properties of electrodeposited Co films on Si(100) and on a polycrystalline Cu substrate has been investigated. Co films of 100-nm thickness on Si and on Cu exhibit similar magnetic properties. It appears that the grain size and the interfacial roughness of the Co films do not influence significantly the magnetic properties, while the crystallographic structure plays a predominant role. We have shown that the pH of the electrolyte influences the fraction of the hcp and fee phase in the Co film and therefore tunes its magnetic properties. (C) 2000 Elsevier Science B.V. All rights reserved.