Copper powders were coated by columnar nanostructured silver films by replacement reaction in aqueous system with PVP and citric acid at room temperature. The dense and uniform silver coating layer was obtained by strictly controlling Ag/Cu ratio. With different Ag/Cu ratio, different content of Ag in the composite can be obtained. The mechanism of composite powders formation and their characteristics were discussed in detail. It is noted that citric acid and PVP play different roles in preparing high quality Cu-Ag composite powders. (C) 2012 Elsevier B.V. All rights reserved.