Fiber　supercapacitors　(FSCs)　are　attractive　energy　storage　devices　for　wearable　and　portable　electronics.　However,　it　still　remains　a　great　challenge　to　achieve　high　volumetric　specific　capacitance　without　sacrificing　the　rate　capability　of　FSC.　Here,　we　demonstrate　a　novel　hierarchically　nanostructured　hybrid　fiber　with　thin　polyaniline　(PANI)　layer　anchored　on　the　highly-conductive　poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)　(PEDOT:PSS)　hydrogel　framework　as　electrodes　for　FSCs.　The　hybrid　fiber　was　prepared　via　hydrothermal　assembly　of　a　commercial　PEDOT:PSS　dispersion　followed　by　acid　treatment　and　in-situ　chemical　polymerization　of　aniline.　The　incorporation　of　highly-electroactive　PANI　boosts　the　whole　capacitance　of　hybrid　fiber;　the　robust　PEDOT　hydrogel　framework　provides　abundant　ions　diffusion　channels　and　rapid　electron　transfer　pathways,　improving　the　utilization　efficiency　and　the　kinetics　of　pseudocapacitance　reaction　of　PANT　Attributed　to　the　synergistic　effect,　the　PEDOT/PANI　hybrid　fiber　in　FSC　exhibits　high　volumetric/areal　specific　capacitance　(554.1　F　cm(-3)　or　740.0　mF　cm(-2)　at　5　A　cm(-3)),　excellent　rate　performance　and　good　electrochemical　stability.　The　flexible　FSC　device　delivers　a　high　volumetric　energy　density　of　11.9　mWh　cm(-3)　at　981.4　mW　cm(-3)　and　areal　energy　density　of　15.8　mu　Wh　cm(-2)　at　1310.5　mu　W　cm(-2),　outperforming　most　of　the　reported　counterparts.　The　well-designed　PEDOT/PANI　hybrid　fiber　based　FSC　hold　a　great　potential　for　powering　the　next-generation　wearable　and　portable　electronics.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.