We report the preparation and supercapacitive properties of a novel composite electrode material based on carbon nanofiber (CNF) and poly(tetrahydro[1,4] dioxino[2,3-b] thieno[3,4-e][1,4] dioxine) (PTDTD) for electrochemical energy storage applications. The CNF/PTDTD composite electrode was directly prepared by electrodeposition of PTDTD on the CNF coated substrate without any binder or conductive additives. The symmetric solid-state supercapacitor device was assembled by using these CNF/PTDTD composite electrodes. In addition, CNF/CNF and CNF/poly(3,4-ethylenedioxythiophene) (PEDOT) symmetric supercapacitor devices were also fabricated to make a detailed performance comparison. The electrochemical characteristics of all supercapacitor devices were comprehensively evaluated by CV, GCD and EIS measurements. The CNF/PTDTD composite electrodes delivered a maximum specific capacitance of 332 F g(-1), energy density of 166 W h k g(-1), power density of 4.9 kW kg(-1) and an excellent cycling stability with 89% capacitance retention after 12 500 cycles at 2 mA cm(-2) current density while CNF/PEDOT electrodes were able to reach a specific capacitance of 254 F g(-1), energy density of 128.8 W h kg(-1) and power density of 5.45 kW kg(-1) in those supercapacitor devices. These results confirmed that PTDTD has significant potential to be a good alternative redox-active material and CNF/PTDTD composite structure is a promising candidate for supercapacitor applications.