Poly(methyl methacrylate)/multiwalled carbon-nanotube (PMMA/MWNT) nanocomposites were prepared via in situ polymerization induced by nickel(II) acetylacetonate/methylaluminoxane ([Ni(acac)(2)]/MAO) catalyst. The incorporation of the MWNT into the PMMA increased the glass transition temperature and thermal decomposition temperature. The solution-casted films of the nanocomposites dissolved in methylene chloride exhibited very high transparency. The introduction of MWNT decreased the syndiotacticity of the resultant PMMA. The storage modulus of the composite increased significantly with increased MWNT content in the PMMA matrix, which was much higher than that of PMMA/clay nanocomposites at the same wt % of filler contents. The PMMA-rich layer which usually formed on the coating surface due to the surface tension and wetting characteristics of the MWNT/PMMA matrix provided excessive interactions between the large surface area nanotubes and the PMMA matrix.