Polyethylene (PE)-boehmite nanocomposites were prepared by means of metallocene/MAO-catalyzed in-Situ polymerization of ethylene in the presence of boehmites, which were rendered organophilic by modification with carboxylic acids Such as stearic acid and undecylenic acid. Such organoboehmites are readily dispersed in the polymerization media Such as toluene. Polymerization activity, filler dispersion and mechanical properties of the nanocomposites were investigated as a function of type and concentration of [lie organoboehmites. The catalyst activity of different metallocenes (Cp2ZrCl2 and rac-Me2Si(2-Me-benz[e]-Ind)(2)ZrCl2) was increased up to 100% in the presence of organoboehmite fillers. The dispersion of nanoboehmites, as evidenced by TEM Studies, was dependent upon the content of the carboxylate modifier. At 20 wt.% carboxylate content uniform dispersions of organoboehmite particles with average particle sizes smaller than 100 tun were obtained. According to stress-strain measurements, the Young's modulus increased with increasing boehmite content without sacrificing high elongation at break. (C) 2007 Elsevier Ltd. All rights reserved.