Porous carbon materials derived from various biomasses have aroused intense interest from the scientific community due to their low cost, abundant resources, eco-friendliness and easy fabrication. Herein, three-dimensional honeycomb-like hierarchical structured carbon (HSC) has been fabricated by one-step carbonization/activation of abundant and low cost bacterial cellulose for ultrahigh energy density supercapacitors. Benefitting from its interconnected honeycomb-like hierarchical and open structure with a high specific surface area, the prepared HSC exhibits a superhigh specific capacitance of 422 F g⁻¹ at 2 mV s⁻¹ with remarkable rate performance (73.7% at 500 mV s⁻¹) in 6 M KOH aqueous electrolyte. Meanwhile, the symmetric supercapacitor could deliver a high energy density of 37.3 W h kg⁻¹ in 1 M Na₂SO₄ aqueous electrolyte. To evaluate the practical application, an asymmetric supercapacitor fabricated with NiCoAl-layered double hydroxide as the positive electrode and HSC as the negative electrode achieves a conspicuously high energy density of 100 W h kg⁻¹ and could still retain 33 W h kg⁻¹ even at a high power density of 36.8 kW kg⁻¹, which is highly comparable with or even higher than those of the previously reported asymmetric supercapacitors in aqueous electrolytes. Furthermore, our asymmetric supercapacitor exhibits excellent cycling stability along with 113% capacitance retention after 10 000 cycles. Such spectacular results will shed new light on biomass-derived carbon materials for the next generation of ultrafast energy storage devices with high energy density and excellent long cycle life.