Amorphous iron oxide (IO) nanoparticles (NPs) with excellent water-solubility were synthesized at room temperature without the presence of any solvents. The obtained nanoparticles were characterized by FTIR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), EDS (energy dispersive X-ray spectroscopy), X-Ray photoelectron spectroscopy (XPS), and TEM (transmission electron microscopy). T-2-weighted MRI images of citrate-coated NPs showed that the magnetic resonance signal is enhanced significantly with increasing nanoparticle concentration in water. Advantages of this method rely not only on the simplicity and nontoxicity but also on the low cost, highly suitable for further applications. These results indicate that the citrate-coated NPs have great potential for application in MRI as a T-2 contrast agent.