Here, we revealed the effect of particle size of the nanoscale SiO2 on catalytic and characteristic properties of LLDPE/nano-SiO2 composites synthesized via the in situ polymerization with a zirconocene/MAO catalyst. In the experiment, SiO2 (10 and 15.nm) was first impregnated with MAO. Then, copolymerization of ethylene/l-hexene was performed in the presence of nano-SiO2/MAO to produce LLDPE/nano-SiO2 composites. It was found that the larger particle exhibited higher polymerization activity due to fewer interactions between SiO2 and MAO. The larger particle also rendered higher insertion of 1-hexene leading to decreased melting temperature (Tm). There was no significant change in the LLDPE molecular structure by means of C-13 NMR. (c) 2006 Elsevier Ltd. All rights reserved.