Ag-10Cu in situ filamentary composite was prepared by hot extrusion and cold wire drawing. The as-cast and as-extruded Ag-10Cu alloys consist of Ag matrix, (Ag+Cu) eutectic and Cu precipitates which will become a structure of Ag matrix and Cu filaments after heavy deformation. The size of Cu filaments, transformed from coarse Cu precipitates, changes with drawing strain, and their relationship can be expressed as d=doexp(–0.144η). Two-stage strengthening characteristics were obtained and the strengthening mechanism of this composite was discussed. A combination of ultimate tensile strength approaching 1 GPa and electrical conductivity exceeding 60% IACS can be achieved for this composite. The effect of intermediate heat treatment was also discussed