Enhanced photovoltaic performance of a DSSC using graphene-TiO2 photoelectrodes prepared by our recent in situ simultaneous reduction-hydrolysis technique (Adv. Funct. Mater., 2012, DOI: 10.1002/adfm.201202349, in press) was achieved. The DSSCs based on the G-TiO2 nanocomposites improved their overall energy conversion efficiency to 7.1%. The results prove that the promoting effect of graphene is strongly dependent on its content; namely, the efficiency of DSSCs increases and then decreases with increasing graphene content in TiO2-graphene composites. Excessive graphene in the nanocomposite leads to a decrease of the light harvest of dye molecules and thus a negative effect on the power conversion efficiency of DSSCs.