Poly-methylmethacrylate/Mg-Al layered double hydroxide (PMMA/LDH) based nanocomposites have successfully been synthesised with varying LDH content by in situ polymerisation technique and systematically studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT IR), UV-Visible spectroscopy and microscopic (FE SEM and HR TEM) analysis. In particular, thermogravimetric analysis (TGA) and gas barrier properties measurement were carried out to assess the suitable application of these materials. The thermal property of PMMA/LDH composites was compared with neat PMMA and an enhancement in thermal stability was noticed with gradual increase in LDH content in the composite. Gas permeability measurement data showed significant decrease in oxygen permeability value of the PMMA/LDH nanocomposites in comparison to the pristine PMMA. Enhancement in thermal stability along with significant reduction in oxygen permeability of PMMA upon composite formation indicate the possible application of these materials in packaging industries.