Polyethylene-clay nanocomposites were prepared by melt compounding various combinations of a maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA), a linear low density polyethylene (LLDPE), and two organoclays. The two types of organoclay were selected to show the effect of the number of alkyl groups attached to the nitrogen of the organic modifier on exfoliation and improvement of mechanical properties. Nanocomposites derived from the organoclay having two alkyl tails, M-2(HT)(2), exhibited better dispersion and improvement of mechanical properties than nanocomposites based on the organoclay having one alkyl tail M-3(HT)(1). This result is the opposite of what is observed for nylon-6 nanocomposites. In addition, the theological properties and gas permeability of the nanocomposites derived from the organoclay having two alkyl tails, M-2(HT)(2) were investigated. Both melt viscosity and melt tension (melt strength) increased with increased content of clay (MMT) and LLDPE-g-MA. Gas permeability was decreased by the addition of MMT. (C) 2004 Elsevier Ltd. All rights reserved.