The polyethylene-clay nanocomposites were prepared by the in situ graft copolymerization of styrene containing twin-benzyldimethyldioctadecylammonium bromine modified montmorillonite (TBDO-MMT) in polyethylene with dicumyl peroxide (DCP) as an initiator in molten state. XRD and TEM analysis indicated that intercalated polyethylene/MMT nanocomposites are obtained. The mechanics performance, crystal behavior, thermal properties, and the effect of MMT contents on PE/MMT nanocomposite were also studied. As comparison, polyethylene/montmorillonite composites prepared by a simply melt compounding without styrene were studied as well. (c) 2006 Wiley Periodicals, Inc.