For fabricating more inexpensive thin film solar cells, CuInS2 thin films were prepared by RF sputtering from binary compounds (Cu2S and In2S3). From EPMA analyses, composition of the thin films was varied with changing the mixing ratio ＇x＇ (x = [Cu2S]/[In2S3]). X-ray diffraction studies showed that the thin film sputtered from the target with the mixing ratio of x = 1.5 had a single phase with chalcopyrite structure. In this case, CuInS2 thin films showed higher optical absorption coefficients and a band gap of 1.52 eV, suitable for absorbing incident solar spectrum.