The electrochemical capacitance behavior of a packed bed electrochemical reactor (PBER) toward phenol electro-oxidation in aqueous solution was studied. In the absence of phenol, a decrease in the response current (i) coupled with an increase of the specific capacitance (C (s) ) was obtained for PBER compared with a flat-bed electrochemical reactor. However, following intercalation of phenol, simultaneous improvement of i, and reduction of C (s) were observed. The reasons for the former were ascribed to an increased resistance, an abundant pore structure for charge, and electrolyte transportation owing to the packing of the fixed granular active carbon (GAC) filler, whereas anode extension and formation of the polyoxyphenylene film on the anode and the GAC surface were responsible for the latter. Although significant attenuation (42.06 % after 300 cycles at current density 1.90 mA cm(-2)) of C (s) was observed for PBER in the long cycle test, the non-negligible C (s) value (30.86 mF cm(-2)) holds great promise for pulsating power supplies. An equivalent circuit associated with electrochemical capacitance and resistance distribution was proposed, which gives an exhaustive explanation of the electrical characteristics during the phenol electro-oxidation process.