The porous carbon-derived biomass is inexpensive and ecofriendly, making them the promising electrode materials for supercapacitors. In this work, oxygen-enriched porous carbon is derived from Platanus fibers via a carbonization and activation process using KMnO₄ as the activator. KMnO₄ plays the role of both activator and modifier. The obtained porous carbon possesses high oxygen content and shows tube-like hollow structures. The sample OPF-700-3 exhibits a high oxygen content (13.79%), total pore volume (0.64 cm³ g⁻¹), and specific surface area (1406 m² g⁻¹). The prepared OPF-700-3 electrode material presents a high specific capacitance (318 F g⁻¹ at 0.5 A g⁻¹) and retains 181 F g⁻¹ even at 50 A g⁻¹ in a three-electrode system. The as-prepared symmetric supercapacitors have a high specific capacitance (252 F g⁻¹) and an excellent cycle stability (96.5% specific capacitance retention after 20 000 cycles). Furthermore, it has a high energy of 7.04 Wh kg⁻¹ at a power density of 22.66 W kg⁻¹. This study provides a facile, inexpensive, and environmentally friendly method for biomass prepared from porous carbon, which are used as electrode materials present excellent electrochemical performances.