A new sodium ferrous orthophosphate Na (x) Fe-4(PO4)(3) (1.1 a x a 1.2) with P2(1)/n symmetry has been successfully synthesized via a solid-state reaction for the first time. The structure consists of FeO5 pyramids, FeO6 octahedron, and PO4 tetrahedra which form large six-sided tunnels along direction and three- or four-sided tunnels running along direction. When evaluated as the anode materials for sodium-ion batteries, the first discharge and charge capacities of 553 and 264 mAh g(-1) for Na1.1Fe4(PO4)(3)/C and 583 and 315 mAh g(-1) for Na1.2Fe4(PO4)(3)/C, respectively, can be obtained at 10 mA g(-1) current density. Compared to the Na1.1Fe4(PO4)(3)/C, Na1.2Fe4(PO4)(3)/C exhibits a better cycling performance, where the charge capacity of about 100 mAh g(-1) can still be maintained after 15 cycles. The electrode kinetics are investigated further by the electrochemical impedance spectroscopy.