In this work, Cu 3−y Ag y Sb 1−x Ge x Se 4 (x = 0, 0.04, 0.06, 0.08, 0.10, 0.12; y = 0, 0.1, 0.2, 0.3, 0.4) is fabricated using a high-temperature melting process, and the thermoelectric properties are investigated in the temperature range of 300−700 K. As a result, a remarkable improvement in thermoelectric performance of Cu-based ternary thermoelectric materials is achieved here. Ge doping increases the carrier concentration leading to a decrease in electrical resistivity; Ag alloying can reduce thermal conductivity significantly and enhance the power factor. Consequently, a maximum figure of merit, 0.95, is obtained for Cu 2.7 Ag 0.3 Sb 0.94 Ge 0.06 Se 4 and Cu 2.6 Ag 0.4 Sb 0.94 Ge 0.06 Se 4 at 700 K, which is higher than most reported Cu 3 SbSe 4 -based systems.