This paper presents a method for the chemical synthesis and characterization of Fe₃O₄ magnetic nanoparticles (MNPs). In the work, MNPs were fabricated by chemical co-precipitation. The stoichiometric ratio of Fe²⁺/Fe³⁺ was 2:3, and polyethylene glycol 2000 (PEG-2000) was chosen as the dispersant. Isolated single MNPs were obtained from the diluted solution of MNPs dried on a clean silicon wafer surface. The X-ray diffractometer (XRD), scanning electron microscope (SEM) and magnetic force microscope (MFM) were used to characterize the Fe₃O₄ MNPs. The fabricated Fe₃O₄ MNPs were paramagnetic and able to be separated from the solution by a magnet. The experiment results have shown that this method can obtain the decentralized MNPs with the average diameter of 99.6 nm for different potential applications.