The novel exfoliated polymer nanocomposites (PMMA/MgFe(DS)-LDH) were synthesized by in situ polymerization based on poly(methyl methacrylate) (PMMA) and dodecyl sulfate-intercalated MgFe-layered double hydroxide (MgFe(DS)-LDH). The participation of Fe(3+) ion is found to play an important role in the improvement of thermal stability of nanocomposites with small inorganic loading and well-dispersed inorganic components. The thermal degradation mechanism was discussed. (c) 2008 Elsevier Ltd. All rights reserved.