In this study, NdFe12Nx magnetic powders were modified using 3-aminopropyltriethoxysilane coupling agent (KH550). The phase compositions, antioxidant properties, and magnetic properties of NdFe12Nx magnetic powder before and after surface modification were investigated by X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer, respectively. The possible mechanism of the surface modification was also discussed. The results showed that the silane coating prevented the NdFe12Nx powders from corrosion and oxidation, thereby maintaining the durability and long term stability. Although the surface modification using KH550 reduced the magnetic properties to a certain extent, it played an important role in improving the oxidation resistance of NdFe12Nx powders. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.