CuInSe 2 (CIS) nanoparticles were synthesized by a solution process using copper chloride, indium chloride and selenium as the precursors and oleic acid as the solvent. The synthesized CIS nanoparticles were characterized by XRD, SEM-EDS, and UV–vis spectroscopy. The lattice parameters of the CIS nanoparticles increased with increasing reaction temperature. The band gap energies of the CIS nanoparticles ranged from 0.954 to 0.984eV. Ga could not be incorporated into the CIS nanoparticles regardless of high Ga concentration. The atomic ratio of Cu in the CIS nanoparticles increased with increasing Ga content in the precursor solutions, while those of Se and In decreased.