Oxygen　functional　groups　on　a　commercial　activated　carbon　were　modified　by　(NH4)(2)S2O8　oxidation　and　subsequent　annealing　at　different　temperatures.　The　effects　of　the　surface　modification　on　the　electrochemical　performance　as　supercapacitor　electrodes　were　investigated　by　XPS,　FTIR,　argon　adsorption　and　electrochemical　tests.　Results　indicate　that　the　oxygen　functional　groups,　especially　carboxyl　and　carbonyl　groups　improved　the　wettability　of　the　pore　surfaces,　increased　the　electrolyte　diffusion　rate　into　the　electrode　and　increased　the　specific　capacitance　by　an　additional　pseudo-capacitance　in　a　6　mol/L　KOH　aqueous　electrolyte.　An　excess　oxygen　content　blocked　the　pores,　leading　to　poor　electrochemical　performance,　but　annealing　at　300　degrees　C　in　an　inert　atmosphere　increased　the　specific　capacitance　and　improved　the　rate　performance　in　a　6　mol/L　KOH　aqueous　electrolyte.　In　a　1　mol/L　Et4NBF4/PC　organic　electrolyte,　however,　oxygen　functional　groups　introduced　by　(NH4)(2)S2O8　oxidation　reduced　the　specific　capacitance　and　annealing　at　700　degrees　C　to　reduce　their　content　effectively　increased　the　specific　capacitance.