©2014 The Japan Institute of Metals and Materials. CuGaTe2has a large thermoelectric (TE) figure of merit (ZT) at high temperatures, i.e., ZT = 1.4 at 950 K. However, at lower temperatures, the ZT values are smaller. One reason for this is that CuGaTe2 has a high lattice thermal conductivity (Klat) at lower temperatures. One known method for reducingKlatis manipulating the microstructure of the bulk material. Therefore, herein, the grain-size effect on the TE properties of CuGaTe2bulk samples produced by ball milling and hot pressing was investigated. Although Klatdecreased with grain size, a simultaneous decrease in the Seebeck coefficient occurred, leading to no overall improvement in ZT.