We report on the effects of thermal processing on the microstructure and composition of a system with overall stoichiometry of 3Cu:1Sb:3Se with the aim of producing single-phase Cu3SbSe3. It was found that slow cooling from the melt produced a multiphase material consisting of Cu2Se and CuSbSe2, but devoid of Cu3SbSe3. Cooling rapidly from the melt resulted in three-phase microstructures consisting of Cu2Se, CuSbSe2, and Cu3SbSe3. Subsequent annealing of the three-phase material between 325 and 400 A degrees C shifted the composition toward nearly pure Cu3SbSe3-the target compound of this work. The kinetics of the transformation into Cu3SbSe3 was successfully described using a modified Avrami model which suggests that diffusion is the rate-controlling step. Values of Young's modulus and hardness, obtained by nanoindentation, are reported for Cu2Se, CuSbSe2, and Cu3SbSe3.