Developing an efficient approach of transforming biomass waste to functional carbon-based electrode materials applied in supercapacitor offers an important and high value-added practical application due to the abundance and considerable low price of biomass wastes. Herein, a hierarchical carbon functionalized with electrochemical-active oxygen-containing groups was fabricated by microwave treatment from the biomass waste of camellia oleifera. The obtained mesoporous carbon (MAC) owns nanosheet morphology, rich mesoporosity, large surface area (1726 m2/g) and very high oxygenic functionalities (16.2 wt%) with pseudocapacitive activity. Prepared electrode of supercapacitor and tested in 2.0 M H2SO4, the MAC exhibits an obvious pseudocapacitive activity and achieved a superior supercapacitive performance to that of directly activated carbon (DAC-800) including high specific capacitance (367 F/g vs. 298 F/g) and better rate performance (66% vs. 44%). The symmetrical supercapacitor based on MAC shows a high capacity of 275 F/g, large energy density of 9.55 Wh/kg (at power density of 478 W/kg) and excellent cycling stability with 99% capacitance retention after 10000 continuous charge-discharge, endowing the obtained MAC a promising functional material for electrochemical energy storage.