There are a few reports on the composites of CuInS2-Cu2S, AgInS2-Ag2S, and CdIn2S4-CdS and this can have various reasons such as reporting no suitable method to synthesize their composites, lack of knowledge about their amazing properties and pay too much attention to pure materials. In this work In2S3 and CdS nanoparticles were prepared by a simple hydrothermal method and then annealed at 500 °C for 2 h in an Ar gas until CdIn2S4(CdIS)-CdS nanocomposites were formed. The as-synthesized nanocomposite was extensively characterized by XRD, EDS, SEM and DRS. The obtained XRD results show that for synthesizing CdIS-CdS nanocomposite without oxide impurities, the presence of argon gas is required. Afterwards, efficiency of the as-synthesized CdIS-CdS nanocomposite in quantum dot-sensitized solar cells (QDSSCs) was evaluated. For this purpose, the as-prepared CdIS-CdS nanocomposites were deposited on TiO2 by doctor’s blade technique and electrophoresis deposition was used for fabrication of TiO2 layer on the FTO glass substrate. Using CdIS-CdS nanocomposite led to obtaining 1.71% cell efficiency that in comparison with pure CdS (0.97%) and CdIn2S4 nanoparticles (95%), efficiency improvements of 76% and 80% were respectively achieved.