The iron-containing electrode material is a promising candidate for low-cost Na-ion batteries. In this work, the electrochemical properties of Fe3O4 nanoparticles obtained by simple hydrothermal reaction are investigated as an anode material for Na-ion batteries. The Fe3O4 with alginate binder delivers a reversible capacity of 248mAhg−1 after 50 cycles at a current density of 83mAg−1 (0.1C), while the electrode using polyvinylidene fluoride binder shows a gradually capacity fading to 79mAhg−1 after 50 cycles. The high electrochemical performance can be ascribed to both the nano size of Fe3O4 and excellent binding ability of alginate binder which can buffer large volume change. The mechanism of conversion reaction for Fe3O4 is also tracked by combining electrochemical impedance spectroscopy analysis and magnetization measurement after electrochemical cycling. Finally, the Na-ion full cell consisting of the Fe3O4-alginate anode and the Na3V2(PO4)3/graphene cathode is assembled to demonstrate performance of the Fe3O4 anode for Na-ion batteries.