Structure, thermal properties, and influence of layered double hydroxide (LDH) fillers on photocrosslinking behavior of high-density polyethylene (HDPE)/LDH nanocomposites have been studied in the present article. The X-ray diffraction and transmission electron microscopy analysis demonstrate that the completely exfoliated HDPE/LDH nanocomposites can be obtained by controlling the organomodified LDH loading via melt-intercalation. The data from the thermogravimetric analysis show that the HDPE/LDH nanocomposites have much higher thermal stability than HDPE sample. When the 50% weight loss was selected as a comparison point, the decomposition temperature of HDPE/LDH sample with 5 wt % LDH loading is similar to 40 degrees C higher than that of HDPE sample. The effects of UV irradiation on the HDPE/LDH nanocomposites show that the photoinitiated crosslinking can destroy the completely exfoliated structure to form the partially exfoliated structure, which decreased the thermal stability of the nanocomposites. However, the thermal stability of photocrosslinked samples can increase with increasing the UV irradiation time. The effect of LDH loading on the gel content of UV irradiated nanocomposites shows that the LDH materials can greatly absorb the UV irradiation and thus decrease the crosslinking efficiency. (c) 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3165-3172, 2006.