We used low-cost pomelo peel (PP) as a biomass-derived porous activated carbon to fabricate a high energy density symmetric supercapacitor. The porous activated carbon was prepared from the pomelo peel (PP) via pyrolysis and a KOH activation process, followed by heat treatment under an argon atmosphere. The resulting porous carbon possesses a very high specific surface area (2105 m² g⁻¹) and abundant oxygen functionalities, which lead to a wide voltage window of 1.7 V, a specific capacitance of 43.5 F g⁻¹ and a high energy density of 17.1 W h kg⁻¹ for the as-assembled AC//AC symmetric supercapacitor. These impressive electrochemical characteristics may indicate the PP to act as a new biomass source of carbonaceous materials for low-cost and high performance electrical energy storage devices.