Counter electrodes (CEs) are fundamentally important components of quantum-dot-sensitized solar cells (QDSSCs), helping to transfer electrons from external circuit to electrolyte and acting as catalysts. In this work, Co0.85Se/RGO composite films were synthesized via one-step solvothermal process. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS) were utilized to characterize the structure, morphology and elemental distribution of the composite CEs. The photovoltaic studies revealed that the composite CEs could yield PCE reaching 2.6% when assembled with CdS/CdSe/TiO2 photoanodes for QDSSCs. EIS and Tafel polarization indicated that the enhanced performances were due to combined high catalytic properties of Co0.85Se with better electron conductivity of RGO.