Humic acid is creatively selected as an anode material in sodium ion batteries. Bio-based carbon fibers (H-CF) are fabricated from polyacrylonitrile (PAN) - humic acid (HA) via simple eletrospinning followed by stabilization and carbonization. The heat-treatment temperature (HTT) is optimized based on analysis of material structures and electrochemical performances. Due to unique composite networks and oxygenic functionalities, the H-CF anode obtained at 1300 degrees C has a large reversible capacity of 261.3 mAh g(-1) (current density: 0.02 A g(-1), initial efficiency: 69.6%). The anode also presents good cycle stability (249.6 mAh g(-1) reversible capacity at 0.1 A g(-1) with capacity retention of 92.8% over 100 cycles) and good rate capability (208.6 mAh g g(-1) at 0.2 A g(-1) and 81.7 mAh g g(-1) at 1 A g g(-1)). It is proved that humic acid can serve as a robust precursor for high-performance anode of sodium ion batteries. (C) 2017 Elsevier Ltd. All rights reserved.