Solid solution is an effective way to optimize thermoelectric performance because of the enhanced phonon scattering from point defect. In this article we describe the synthesis and discuss thermoelectric properties of Cu1-xAgxInTe2 solid solutions (x = 0, 0.05, 0.15, 0.30, 0.50). The effect of the substitution of Ag for Cu site on the microstructure and thermoelectric performance in CuInTe2 is investigated. The enlarged Seebeck coefficient coupled with reduced electrical conductivity is observed due to the diminished carrier concentration upon Ag substitution. Meanwhile, the lattice thermal conductivity is significantly depressed in solid solutions due to the strong phonon scattering. As a result, a zT value of 1.07 is achieved at 823 K with x = 0.05, which is a 90% improvement as compared with that of the pristine CuInTe2. These results demonstrate a valid approach to improve the thermoelectric properties of the compounds in the same family.