The poly(methyl methacrylate) (PMMA)/reactive montmorillonite nanocomposites were prepared by emulsion polymerization. The double bonds were introduced to both the surfaces and interlayers of the montmorillonites to obtain the reactive montmorillonites. The structure of the nanocomposites measured by wide angle X-ray diffraction (WAXD) indicated that the montmorillonites were exfoliated. The average molecular weight of the nanocomposites revealed by gel permeation chromatography (GPC) was larger than that of pure PMMA. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated that the thermal properties of the nanocomposites were enhanced and could be affected by the amount of the reactive montmorillonites. In addition, the tensile properties of the nanocomposites measured by an Instron testing machine improved and the nanocomposites including 3 wt% reactive montmorillonites showed the best tensile strength. The Young's modulus increased with the addition of the reactive montmorillonites. The aging properties of the nanocomposites had an improvement compared with pure PMMA. The optical properties assessed by UV-Visible spectroscopy revealed that the transmittance decreased as the amount of the reactive montmorillonites increased. Finally, the mechanism to prepare PMMA/reactive montmorillonite nanocomposites was proposed. (C) 2015 Society of Plastics Engineers