We report the successful fabrication of the various types of water soluble PEGylated magnetic complexes (PMCs) for magnetism-related biomedical applications. Various types of PMCs were synthesized and tested to accomplish phase transfer from organic to aqueous phase using monomethoxy polyethylene glycol (mPEG)-fatty acid amphiphilic block copolymers (PFs) through conjugation of the hydroxyl group of mPEG with the carboxyl group of fatty acids. We also carefully investigate their colloidal stabilities in aqueous phase according to the ratio of hydrophilic and hydrophobic lengths relying on different types of fatty acids. Synthesized PMCs clearly demonstrated high magnetic sensitivity under magnetic field as magnetic resonance (MR) contrast agents. Furthermore, PMCs exhibited sufficient cell viabilities and excellent cell affinities in an in vitro model. Our results demonstrated that our PMCs possessed the potential for highly efficient magnetism-related biomedical applications such as MR image agents, drug delivery and tracking of cells.