This work investigates the influence of some ammonium quaternary compounds as coupling agent in polyethylene/clay nanocomposites to improve the performance of polyethylene used as packaging barrier material. The 3 wt % of vermiculite used as a nanofiller was added to linear low-density polyethylene (LLDPE) and to linear low-density polyethylene grafted with maleic anhydride (LLDPE-g-MA). The analysis results revealed that the influence of both the clay exfoliation in a polymer matrix and the coupling agents on the barrier properties were significant. Among the coupling agents used, cetylpropyldimethylammonium chloride yielded the best result for vermiculite exfoliation. A reduction of up to 18% in the oxygen-permeability coefficient was observed in the nanocompounds with exfoliated vermiculite. The nanocomposite produced with vermiculite did not prove to be efficient as a moisture barrier against according to the analysis performed. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3695-3700, 2010118636953700