Abstract: In this work,we have synthesized γ-Fe2O3 superparamagnetic nanoparticles by using co-precipitation method.The phase structures,magnetic property and morphology of the resulted bare particles have been characterized by X-ray diffraction (XRD),Vibrating Sample Magnetometer (VSM),Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS).The size of resulted bare particle is about 10nm.Afterwards,we have coated the bare nanoparticles by using polyacrylic acid with different molecular weight.The polymer coated nanoparticles have been characterized by XRD,TEM and DLS as well.Furthermore,the colloidal stability of coated nanoparticles in concentrated salt (NH4Cl) solution and cell-culture medium (high glucose) have been monitored by using DLS.The DLS results show that coated nanoparticles present remarkable colloidal stability,which is an excellent precursor for further biomedical application.