The search for semiconductor-sensitized solar cell (SSC) counter electrode alternatives has been a continuous effort and long ongoing work, while the studies in counter electrode kinetic performance and stability are important to improve the overall efficiency. Here, a ternary chalcopyrite compound CuInS2 is first employed as counter electrode (CE) material for CdS/CdSe cosensitized solar cells. Besides, in order to increase the electron transfer activity at the counter electrode/electrolyte interface and stability, an appropriate amount of active carbon/carbon black mixture is introduced to afford CuInS2/carbon composite electrodes. Electron transfer processes in CuInS2-based electrodes are investigated in detail with the aid of electrochemical impedance spectroscopy and I-E measurement. Up to 4.32% of the light-to-electricity conversion efficiency has been achieved for the CdS/CdSe SSCs with the CuInS2/carbon composite electrode. Besides, a preliminary long-term stability test reveals that the new CuInS2/carbon composite counter electrode exhibits good stability after being kept in the dark at room temperature and without current flow for 1000 h.