A polysulfide electrolyte considering simultaneously the penetration of the electrolyte in a mesoscopic TiO2 film and the ion dissociation in the solution is developed for application in a CdS-sensitized solar cell (CdS-DSSC). A methanol/water (7:3 by volume) solution was found to be a good solvent for fitting the requirement mentioned above. The optimal composition of the electrolyte, based on the performance of the CdS-DSSCs, was found to contain 0.5 M Na2S, 2 M S, and 0.2 M KCl. By using a photoelectrode prepared after 4 cycles of chemical bath deposition, FTO/TiO2/CdS-4, the efficiency of the CdS-DSSC obtained for this polysulfide electrolyte is 1.15% under the illumination of 100% sun (AM1.5, 100 mW cm(-2)). This efficiency is less than that obtained using I-/I-3(-) redox couple (1.84%), mainly caused from the smaller values of fill factor and open circuit potential. However, the US sensitizer is stable and, furthermore, a much higher short circuit current and IPCE (80%) are obtained by using the polysulfide electrolyte. (C) 2008 Elsevier B.V. All rights reserved.