A simple one-step method to synthesize carbon-coated Fe₃O₄ composites with complex pine-tree-leaf structures has been developed. As revealed in FESEM and TEM analysis, the Fe₃O₄ nanoparticles were self-assembled to chains-like structures, which were coated by carbon shells with a thickness of about 150 nm, and the needle-like pine-tree-leaf organization grown perpendicular to the central stems are carbon nanorods. Some important preparative parameters related to the synthesis have been identified and investigated with some designed experiments. Ferromagnetic properties of the carbon-coated Fe₃O₄ composites with pine-tree-leaf structures have been further differentiated for the different structures, and the results show that the saturation magnetization value (18.4 emu g⁻¹) is lower than that of bulk Fe₃O₄, and the coercivity value (142.3 Oe) is much higher than that of the bulk Fe₃O₄.