In this study, a magnetic demulsifier, called M-DMEA, was prepared by "one-pot" synthesis through the pyrolysis of ferric triacetylacetonate (Fe(acac)(3)) in DMEA 1231, which is a type of polyether demulsifier used in oil fields. The morphologies and phase compositions of the M-DMEA nanoparticles were determined by transmission electron microscopy and X-ray diffraction, respectively. The presence of surface coating was confirmed by using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analyses (TGA). Magnetic property was measured by vibrating sample magnetometer. The demulsification of M-DMEA for treating oily wastewater produced from polymer flooding (OWPF) was investigated. It was found that the oil removal of M-DMEA reached 96.0 % at the concentration of 4.0 g/L. In addition, M-DMEA can be recycled and reused by using an external magnet. The results showed that there was a significant decrease in the oil removal after two cycles because the polymer residue remaining in OPWF, namely partially hydrolyzed polyacrylamide (HPAM), was adsorbed onto the surface of M-DMEA.