The radiation grafting of styrene or methyl methacrylate onto MgO has been investigated. The graft products were characterized by IR spectrum, X-ray diffraction and pyrolysis gas chromatography. It is shown that MgO-g-MMA graft copolymer and PMMA mixed with MgO have absorption peaks at 1380 cm,-1, and 1430~1480 cm,-1, in IR spectra respectively. For MgO-g-MMA graft copolymer, the fourth peak is obviously observed in pyrolysis gas chromatography, On the X-diffraction pattern there are another five crystal peaks except the original five crystal peaks of MgO, their spacing of lattice are 4.7702 Å, 2.3618 Å, 1.7926 Å, 1.5703 Å and 1.3084 Å respectively. It is evident that the crystal lattice of MgO affects the regularity of PMMA polymer. It is believed that the radiation product is the graft copolymer onto inorganic compound with chemical bonds rather than the mixture of polymer and inorganic compoumd. The molecular weight of graft copolymer is higher than that of homo-polymer, but the molecular weight distribution is broader in the graft copolymer. The adheson between MgO and polyethylene is enhanced after radiation grafting of Vinyl monomer.