Despite the fact that Co3O4 nanomaterials have gained much attention due to their excellent electrochemical properties, the poor conductivity and catalytic reduction ability for I-3 ion hinder their application as counter electrode (CE) of dye sensitized solar cells (DSSCs). Herein, a facile ion exchange approach is developed to prepare S-doped Co3O4 nanosheet. S doping strategy significantly improves the catalytic activity of Co3O4 nanosheets for the reduction of I-3 ion and their charge transport ability. For the sake of doping S into Co3O4 and rGO simultaneously, the similar wet chemical process is adopted in the presence of graphene oxide (GO) to synthesize S-doped Co3O4/reduced graphene oxide (rGO) composites. The power conversion efficiency (PCE) of Co3O4-DSSC is only 1.98%. Using S-doped Co3O4 as CE, the PCE can be dramatically improved to 6.76%. Moreover, the S-doped Co3O4/rGO-DSSC shows higher PCE (8.24%) than that of Pt (7.79%). Electrochemical measurement results indicate that the S-doped Co3O4/rGO composites not only show excellent electrocatalytic activity, but also show high cycling stability. The outstanding improved performance of DSSCs with S-doped Co3O4 nanosheet and S-doped Co3O4/rGO composite as CEs demonstrates that the surface atomic configurations of CE materials have significant influence on their electrocatalytic activity. (C) 2018 Elsevier B. V. All rights reserved.