Abstract: Sisal microcrystalline cellulose(SMC) prepared from sisal wastes was used as flexible substrate and the manganese dioxide(MnO₂) was deposited on its surface by chemical deposition. Then, the pyrrole monomers were in situ polymerized to obtain the PPy@MnO₂@SMC composite electrodes. The effects of deposition time of MnO₂(10, 20 and 30 min) on the performance of composite electrodes were investigated, and the composite electrodes were used to assemble supercapacitors. The composite electrodes were characterized by field emission scanning electron microscopy(SEM) and X-ray diffraction(XRD), and the electrochemical properties were analyzed by cyclic voltammetry(CV), galvanostatic charge-discharge(GCD) and electrochemical impedance spectroscopy(EIS). The SEM and XRD results indicated that the MnO₂ nanosheets were successfully coated on the surface of SMC by chemical depositionand and PPy with amorphous structure was successfully coated on the surface of MnO₂@SMC by in situ polymerization. The electrochemical test results showed that when the deposition time of MnO₂ was 20 min the as-prepared PPy@MnO₂@SMC-2 composite electrode exhibited the best electrochemical performance. At the current density of 0.25 A/g, its specific capacitance was up to 474.3 F/g. The supercapacitor based on PPy@MnO₂@SMC-2 composite electrode had high specific capacitance of 81.6 F/g at current density of 0.25 A/g, and its maximum energy density and power density were 7.3 Wh/kg and 475.7 W/kg, respectively.The supercapacitor showed good flexibility which was proved by the bending test and kept 99.5% of its initial capacitance after 5 000 charge-discharge cycles which indicated its excellent cycle stability. Besides, the corresponding performances about the series and parallel connection and an example of lighting up a lamp demonstrated that the supercapacitor could be applied in practical application.