Electrochemically active redox mediators have been widely investigated in energy conversion/storage system to improve overall catalytic activities and energy storing ability by inducing favorable surface redox reactions. However, the enhancement of electrochemical activity from the utilization of redox mediators (RMs) is only confirmed through theoretical computation and laboratory-scale experiment. The use of RMs for practical, wearable, and flexible applications has been scarcely researched. Herein, for the first time, a wearable fiber-based flexible energy storage system (f-FESS) with hydroquinone (HQ) composites as a catalytically active RM is introduced to demonstrate its energy-storing roles. The as-prepared f-FESS-HQ shows the superior electrochemical performance, such as the improved energy storage ability (211.16 F L-1 and 29.3 mWh L-1) and long-term cyclability with a capacitance retention of 95.1% over 5000 cycles. Furthermore, the f-FESS-HQ can well maintain its original electrochemical properties under harsh mechanical stress (bending, knotting, and weaving conditions) as well as humid conditions in water and detergent solutions. Thus, the strategical use of electrochemically active RMs can provide the advanced solution for future wearable energy storage system. (C) 2020 Elsevier Inc. All rights reserved.