One dimensional Fe3O4 sub-microfibers with an average diameter of about 920 nm and length of about 25 mu m were prepared by hydrothermal synthesis in the presence of sodium citrate (Na(3)cit). The physicochemical properties were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). It was found that Fe3O4 crystal nuclei were generated from different Fe2+ citrate complexes under hydrothermal conditions and Na(3)cit as a capping agent promoted the formation of Fe3O4 microfibers. The Fe3O4 nanocrystals grew along the (1 1 0) axis on the exposed (1 1 1) facet, and then further formed microfibers via an oriented attachment mechanism during the collisions. Polyvinylpyrrolidine (PVP) was more conducive to microfibers growth in comparison to polyethyleneglycol 4000 (PEG-4000), cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SOS). The electrochemical measurements show that the Fe3O4 sub-microfibers had a specific capacitance of 117.6 F g(-1) with good cycling performance. (C) 2017 Published by Elsevier Inc.