Design and fabrication of structurally optimized electrode materials using biomass materials has become one of the hottest subjects in the field of electrochemical energy storage. Hollow tubular carbonized kapok fiber/NiO composites are synthesized by a facile hydrothermal and carbonization procedure using kapok fiber as a low-cost template. Owing to their unique microtubular structure, the as-prepared composites exhibit a high specific capacitance of 575.7 F g⁻¹ at current density of 0.5 A g⁻¹. Furthermore, an asymmetric supercapacitor device also has been fabricated using carbonized kapok fiber/NiO composites and commercial activated carbon as the positive and negative electrodes, respectively. Because of its unique structure, high capacitive performance, and complementary potential window, the asymmetric supercapacitor device can be cycled reversibly at a cell voltage of 1.6 V in 1.0 M KOH aqueous electrolyte, delivering a high energy density of 7.5 W h kg⁻¹ at a power density of 64.6 W kg⁻¹. In addition, the asymmetric supercapacitor device also exhibits a superior long cycle life and the capacitance retention of the initial specific capacitance cannot found clearly degeneration after 4000 cycles. It is worth noting that this scalable protocol also can be employed to prepare other microtubular carbon/metal oxide composites with good electrochemical performances.