Magnetite nanoclusters with an average size of about 120 nm have been prepared and allowed to self-assemble into one-dimensional (1D) nanochain structures with the average length about of 2 mu m by a simple magnetic-field-induced (MFI) assembly approach (0.20 T). The constituent, phase, and morphology of these I D nanochains have been characterized by X-ray diffraction and transmission electron microscopy. Magnetic measurement reveals that these I D nanochains are weakly ferromagnetic at room temperature. In this paper, we discuss the influence of magnetization time and strength of external magnetic field on the formation of I D nanochains. We also show that, by changing the amount of hydrogen peroxide in the starting materials, I D nanochains with different interparticle spacing can be obtained. This I D nanochain structure with different interparticle spacing would be an ideal system for the further study of magnetization properties of ID ordered magnetic nanostructures.