Poly (methyl methacrylate)=zirconium dioxide (PMMA=ZrO 2 ) nanocomposites were prepared by the incorporation of ZrO 2 nanoparticles in various proportions (2, 4, 6, 8, and 10%) with PMMA matrix by in situ emulsifier-free emulsion polymerization technique. The structural property of PMMA=ZrO 2 nanocomposites was studied by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The thermal stability of PMMA=ZrO 2 nanocomposites was improved with increasing concentration of ZrO 2 . The electrical conductivity of composites was measured as function of ZrO 2 concentration. The oxygen barrier properties of PMMA=ZrO 2 nanocomposites were measured by using gas permeameter.