Phase equilibrium and microstructure in the ternary PbO-CuO-Ag system has been investigated using differential thermal analysis (DTA), thermogravimetry (TG), scanning electron microscope (SEM), and X-ray diffraction (XRD) techniques. Composition versus temperature diagrams have been established for these systems in air. In the ternary CuO-PbO-Ag system, there is a eutectic reaction CuO + PbO + Ag = L at 750-degrees-C and a composition of 12.07 mol. % Ag, 16.35 mol. % CuO, and 71.61 mol. % PbO. Two immiscible regions near the two binary tie lines PbO-Ag and CuO-Ag were detected. No binary or ternary compound was detected in these systems. SEM and EDS results confirm the presence of two liquid phases and the eutectic point.