A novel method using montmorillonite-AlN (MMT-AlN) composite particles as dopants in polyimide (PI) has been proposed and tested. We choose MMT-AlN as dopants in PI for lamellar structure of MMT and globular structure of AlN and hope such mixed micro-and nano-particles can enhance PI's resistance to corona aging. Our corona aging test result has confirmed our method and a 7% doped PI/MMT-AlN film has corona aging time extended more than 40 times compared with pure PI film. The microstructure changes of PI/MMT-AlN films due to corona aging have been analyzed by multiple surface analysis techniques. The analysis result shows coexistence of mass fractal and surface fractal in the sample films of PI/MMT-AlN. A dense inorganic block layer of MMT-AlN formed on the surface of doped PI films during corona aging is believed to be the mechanism of providing the protection against further corona aging. (C) 2012 Published by Elsevier B.V.