The effects of dicumyl peroxide/vinyltriethoxysilane treatment and nanoclay content were investigated for low-density polyethylene (LDPE)/clay nanocomposites. LDPE was treated with 0.1 phr of DCP with, respectively, 1 phr and 3 phr VTES (System A), and with 0.2 phr of DCP with the same amounts of VTES (System B), and then mixed with different contents (1, 3, and 5 wt%) of modified clay (Cloisite 15A). The morphology and extent of crosslinking, as well as the thermal, mechanical, and thermomechanical properties were studied. X-ray diffraction results of all the VTES-treated LDPE/clay nanocomposites showed an increase in interlayer spacing, which indicates that the polymer chains were intercalated between the clay layers. Transmission electron microscopy micrographs of System B showed some evidence of exfoliated clay layers, indicating that the system exhibited a mixed morphology. The clay-containing samples had better thermal stability than LDPE, but the thermal stability did not differ much for the two systems. VTES observably decreased the melting enthalpy of LDPE, while the presence of clay had little influence on this value. This is somewhat contrary to the gel content results that showed a decrease in the extent of crosslinking in the presence of and with increasing clay content. VTES/DCP treatment and the presence of clay observably changed the dynamic mechanical and tensile behaviour of the LDPE.