Copper silver selenide has two phases: low-temperature semimetal phase (alpha-CuAgSe) and high-temperature phonon-glass superionic phase (beta-CuAgSe). In this work, the electric transport and thermoelectric properties of the two phases are investigated. It is revealed that beta-CuAgSe is a p-type semiconductor and exhibits low thermal conductivity while alpha-CuAgSe shows metallic conduction with dominant n-type carriers and low electrical resistivity. The thermoelectric figure of merit zT of the polycrystalline beta-CuAgSe at 623 K is similar to 0.95, suggesting that superionic CuAgSe can be a promising thermoelectric candidate in the intermediate temperature range. (C) 2014 Elsevier B.V. All rights reserved.