Inorganic/organic composite electrospun fibers have been extensively investigated as adsorbents for the wastewater treatment. In this study, branched polyethylenimine (b-PEI) functionalized magnetic iron oxide (Fe3O4)/polyacrylonitrile (PAN) composite electrospun fiber adsorbent (b-PEI-FePAN) was fabricated and systematically explored for the removal of toxic hexavalent chromium [Cr(VI)]. b-PEI grafted PAN organic component not only acted as the flexible substrate to load Fe3O4 particles but also made a contribution to the improved adsorption capacity. In the batch adsorption test, the maximum adsorption capacity based on Langmuir fitting was 684.93 mg/g, which was higher than most of the reported adsorbents. The removal efficiency could reach above 98% with a dosage of 0.5 mg/mL in the real water samples. Moreover, the filtration efficiency was also above 98.5% even at a high flux of 765 L center dot m(-2)center dot h(-1) in dynamic filtration experiment. According to mechanism analysis, both electrostatic adsorption and reduction action were involved in the Cr(VI) removal processes. These results demonstrate that b-PEI functionalized Fe3O4/PAN composite electrospun fibers have promising potential in water purification field. (C) 2017 Elsevier Inc. All rights reserved.