Based on the three-dimensional porous and flexible scaffold structure of bacterial cellulose (BC) and the excellent conductivity of carbon nanotubes (MWCNT), a self-supporting conductive substrate was fabricated, and then manganese dioxide (MnO2) was electrodeposited on the substrate to construct a novel BC/MWCNT/MnO2 thin film electrode. Among them, the two components are closely combined through hydrogen bonds, synergistically endowing the composite substrate with excellent electrical conductivity and mechanical properties. The porous structure, electrolyte absorption characteristics and bridging structure of the honeycomb active MnO2 nanosheets of the BC/MWCNT composite membrane endow it with excellent electrochemical performance (at a current density of 1 mA cm-2^, its areal and mass specific capacitances reach 1.17 F cm-2 ^{and 200 F g}-1^, respectively) and remarkable cycling stability (the specific capacitance retention is stable at 96% after 10,000 cycles at a current density of 20 mA cm^-2). Such binder-free thin-film electrodes are facile and inexpensive to prepare, and have great potential in the development of flexible energy storage devices.