The effects of preselected six different layered double hydroxides (LDHs) (Zn/Al 4:1 DDS, Mg/Al 2:1 DDS, Zn/Al 2:1 stearate, Mg/Fe 4:1 stearate, Zn/Al 2:1 laurate, and Mg/Fe 4:1 laurate) on the mechanical, thermal, and fire properties of poly(methyl methacrylate) (PMMA) nanocomposites, synthesized by intercalative in situ bulk polymerization, were evaluated. PMMA nanocomposites containing three different LDH concentrations (1, 3, and 5 wt%) were produced, and it was observed that all the nanocomposites with lower LDH concentration (1 wt%) showed a higher elastic modulus than PMMA. However, as the LDH concentration increased, the elastic modulus decreased for all the nanocomposites. It was shown that PMMA/(Zn/Al 2:1 stearate) containing 5 wt% of LDH in its composition exhibited a decomposition temperature about 97 degrees C higher than pure PMMA. According to this study, it was found that it is possible to enhance some mechanical and thermal properties of PMMA using very low LDH concentrations (mass fraction of LDH equal to 1%). LDHs are inexpensive materials based on abundant metals with a simple synthesis method that has a low environmental impact. (c) 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E660E674, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21309