The purpose of this study was to investigate the effect of filler content and aspect ratio on the thermomechanical behavior of unmodified low density polyethylene (LDPE)-based layered silicate clay nanocomposites. LDPE-based nanocomposites, without any polymer modification and with two kinds of clays, one with low aspect ratio (i.e., synthetic laponite -Lp) and another with high aspect ratio (i.e., montmorillonite) were prepared and characterized using dynamic mechanical analysis (DMA). Organosilicates were added at 2, 5 and 10 wt%, respectively. X-ray diffraction (XRD) analysis was performed on composites obtained by dispersing the organosilicates in unmodified LDPE. The LPDE reinforced with organo-montmorillonite (OMt) had better performance in the whole temperature range than those with organo-laponite (OLp). It was concluded that the relatively high aspect ratio OMt can induce superior dynamic mechanical properties to the LDPE polymer compared to lower aspect ratio OLp. This was linked to the higher active surface area and preferential orientation of longer platelets resulting in higher mechanical enhancement. This behavior was more pronounced up to filler contents of 5 wt%. Further increase of the filler content led to more conventional composites, which hindered the reinforcing ability of the silicates. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers