Effects of P and Mg on the electrical conductivity and mechanical properties of Cu-Ag alloys were investigated experimentally. Small addition of these alloying elements decreased the electrical conductivity of Cu alloy greatly, especially for P addition. The maximum amounts of P addition to obtain the electrical conductivity being over 90%IACS was found to be about 0.019wt.%, and in this case recrystallization temperature of the addition was about 450˚C. The tensile strength was not changed significantly by the addition of P. However, for Cu-Ag-P-Mg alloys, P-Mg compound was precipitated by heat treatment at 450˚C for 1 hour. Such a precipitation of P-Mg compound increased the electrical conductivity of the alloy from 47~57%IACS to 72.3~86.6%IACS. (Received January 15, 1998)