Mechanical alloying in the AgCu system by the ball-milling and repeated rolling methods was performed. A super-saturated f.c.c. solid solution was formed in the entire composition range by ball milling. The lattice parameter change due to the super-saturated solid solution formation matched quite well with the reported result obtained by rapid quenching. Upon heating, the super-saturated solid solution decomposed into base silver and copper solutions, resulting in a large reduction of electrical resistivity. © 1991.