Abstract: We report the preparation of nano-nickel particles embedded in poly(methyl methacrylate) matrix in situ by using radiation reduction of nickel ions and radiation induced polymerization of methyl methacrylate simultaneously with Co-60γ-ray. The size, morphology and structure of the nickel-poly(methyl methacrylate) nanocomposites were investigated by X-ray powder diffraction(XRD) and transmission electron microscopy(TEM) analysis and IR spectrum. XRD pattern of nickel-poly(methyl methacrylate) shows that the products are face-centred cubic(fcc) crystalline nickel by the diffraction peaks with 2θvalues of 44.3oand 52.3o, corresponding to the crystal faces of (111) and (200) of fcc crystalline nickel. According to Scherrer′s equation, the mean size of the nickel particles was calculated to be about 7.33 nm. From the IR spectrum of the nanocomposites, it can be seen that the double bond of methyl methacrylate dispeared after irradiation (1640 cm-1) and to be formed polymer. As seen from the TEM image of the sample, the nickel powders consisted of uniform size spherical particles, but small particles had aggregated into secondary particles due to their extremely small dimensions and high surface energy. Therefore, it was difficult to determine precisely the size and the size distribution of the nano-particles by simply viewing theTEM image. Sodium acetate was used as the basic agent, instead of NaOH or NH3·H2O. It can be used to control the pH value of the experimental solution, and does not affect the polymerization of methyl methacrylate. In summary, nickel-poly(methyl methacrylate) nanocomposites have been successfully prepared in one step by γ-irradiation in a heterogeneous system under ambient pressure at room temperature.