CuInS2 thin-films were prepared by sulfurization of Cu-In-O precursors in H2S gas, X-ray diffraction patterns showed that In2O3 phases did not remain in the CuInS2 films sulfurized in a H2S and H-2 atmosphere, whereas In2O3 phase remained in the films sulfurized in a H2S and Ar atmosphere. The performance of CuInS2 solar cells were studied as a function of the H-2 gas pressure during sulfurization. The open-circuit voltage, short-circuit current and fill factor increased with increasing the H-2 gas pressure. The conversion efficiency of the CuInS2 solar cells is strongly affected by the reduction of the Cu-In-O precursors.