Transparent PMMA/ZrO2 nanocomposites were prepared by in-situ bulk polymerization of methyl methacrylate (MMA)/ZrO2 dispersions that were firstly synthesized using nonaqueous synthesized ZrO2 nanocrystals and the function monomer, 2-hydroxyethyl methacrylate (HEMA), as the ligand. The dispersion behavior of ZrO2 nanoparticles in MMA, structure, mechanical and thermal properties of the PMMA/ZrO2 nanocomposites were investigated comprehensively. It was found that ZrO2 nanoparticles were well dispersed in MMA with HEMA ligand, but the MMA/ZrO2 dispersions easily destabilized in air as well as at elevated temperatures. The destabilization temperature of the dispersion is raised by increasing the molar ratio of HEMA/ZrO2 to match the bulk polymerization temperature. The PMMA/ZrO2 nanocomposites showed an interesting chemical structure (namely, highly cross-linked structure even at ZrO2 content as low as 0.8 wt% and hydrogen bonding interaction between polymer matrix and ZrO2 nanoparticles), with enhanced rigidity without loss of the toughness and improved thermal stability. The relationship between the structure and the properties of the PMMA/ZrO2 nanocomposites based on the HEMA coupling agent was discussed. (C) 2010 Elsevier Ltd. All rights reserved.