Multifunctional properties, including energy storage and sensitive diagnosis, are highly demanded for high-performance supercapacitors and sensors. Herein, we describe a facile method for the synthesis of a multitasking bacterial cellulose@Ni(OH)2 paper for use as a flexible supercapacitor electrode with excellent energy storage performance and a sensing platform for high-sensitivity detection of H2O2. Monodispersed surfactant-free Ni(OH)2 particles with a large fraction of edge sites were anchored on the cellulose fiber network, providing a bendable, freestanding, and hydrophilic material, and leading to attractive electrochemical properties. As expected, this flexible electrode exhibited a remarkable areal capacitance of ~2047 mF cm-2 and high flexibility allowing it to be bent to arbitrary angles. As a nonenzymatic H2O2 detection electrochemical electrode, it displayed a fast amperometric response with a linear range of 0.1–12.4 mM, acceptable sensitivity (~3.79 uA mM-1 cm-2), and low detection limit (~0.28 μM, S/N=3). The versatility of the electrode can be demonstrated by its high selectivity in the presence of interfering species, good reliable detection, and also its ability to detect H2O2 in real samples. The simple, low-cost, and general strategy presented herein can be extended to the preparation of other biomass materials and open up new opportunities for flexible electronic devices.