The effects of an intercalating agent on the morphology and thermal and flame-retardant properties of low-density polyethylene (LDPE)/layered double hydroxide (LDH) nanocomposites were studied with Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, microscale combustion calorimetry, thermogravimetric analysis, and mechanical property measurements. X-ray diffraction and transmission electron microscopy demonstrated that after intercalation with stearate anion (SA) or dodecyl sulfate anion (DS), organo-LDH could be nanodispersed in an LDPE matrix with exfoliated structures or intercalated structures simultaneously with partially exfoliated structures, respectively, via melt intercalation. However, the unmodified LDH composites yielded only microcomposites. Microscale combustion calorimetry, thermogravimetric analysis, and dynamic Fourier transform infrared spectra showed the following order for the flame-retardant and thermal properties: LDPE/SA-modified LDH > LDPE/DS-modified LDH > LDPE/NO(3)-modified LDH > LDPE. The higher performance of the LDPE/LDH nanocomposites with respect to flame retardance and thermal stability could be attributed to the better dispersion state of the LDH layers in the LDPE matrix and the greater hindrance effect of LDH layers on the diffusion of oxygen and volatile products throughout the composite materials when they were exposed to burning or thermal degradation. The tensile strength and elongation at break of the LDPE/LDH nanocomposites decreased to some extent because of the decrease in the crystallinity of the LDPE matrix. A transmittance test showed that the transparency of the exfoliated LDPE/SA-modified LDH nanocomposite was very close to that of neat LDPE. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 316-323, 2012