Organophilic nanoclay that was prepared by surface modification of Montmorillonite clay with quaternary ammonium compound was further treated with a surface modifier (silane). Subsequently, different composites were obtained by blending 5 wt % of clay, nanoclay, or silane-treated nanoclay with high-density polyethylene (HDPE) using Brabender Plasticorder. The morphology of the prepared composites was analyzed by using scanning electron microscopy (SEM). In addition, the effect of the surface modifier on the dispersion of clay platelets in the polymer matrix was studied by elemental mapping using energy dispersive X-ray spectroscopy (EDX). Results indicate that the use of silane significantly improves the dispersion of nanoclay, resulting in enhanced mechanical properties. Furthermore, the effect of surface modification on the barrier properties of the nanocomposites was analyzed by determining the long-term permeation rate of xylene and gasoline in blow-molded containers made of HDPE, HDPE/clay composite, HDPE/nanoclay composite, and HDPE/silane-treated nanoclay composite at 23 and 50°C. Of all the composites, the composite with 5 wt.% silane-modified nanoclay showed the best barrier performance. In particular, the barrier property of HDPE/silane-treated nanoclay nanocomposite was found to be 20-folds higher than that of HDPE container. These results suggest the enhanced performance of containers made of HDPE/silane-modified nanoclay for fuel storage in automotive applications.