In this study, phosphorus (P) atoms were doped into reduced graphene oxide (rGO) with two bonding states of P–C and P–O by using annealing treatment. For the first time, the P-doped rGO (PrGO) was employed as the counter electrode (CE) for dye-sensitized solar cell (DSSC). The electrochemical studies reveal that the P doping can effectively enhance the electrocatalytic activity of rGO, and P–C structures have higher electrocatalytic activity than P–O ones for I−/I3 − redox reaction. More significantly, PrGO shows comparable electrocatalytic ability to Pt as CEs. It therefore seems promising for PrGO to be widely used in metal-free DSSCs with low cost and high efficiency.