Thin films of Cu-Co have been electrochemically deposited onto Cu-coated alumina substrates in a single sulfate bath. Electrochemical process parameters are expected to influence the chemical composition and microstructure and hence, physical properties of the films. We have attempted to study and understand the effect of various electrochemical process parameters like bath composition, bath temperature, deposition current density and pH of the electrolyte, along with annealing temperature and time on the magnitude of GMR in Cu-Co films. The maximization of GMR is understood in terms of an optimum distribution of the size and the separation of the magnetic particles via the thermally-induced phase segregation. (C) 2003 Elsevier Science B.V. All rights reserved.