High density polyethylene/Brazilian clay nanocomposites were prepared by the melt intercalation technique. A montmorillonite sample from Boa Vista/PB, Northeast of Brazil, was organically modified with esthearildimethylammonium chloride (Praepagen WB) quaternary ammonium salt. The unmodified and modified clays with the quaternary ammonium salt were introduced in 1, 2, 3 and 5 wt% in a PE polymer matrix. The dispersion analysis and the interlayer distance of the clay particles were obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of tensile and the flammability of the nanocomposites were studied. In general, the mechanical properties of the systems presented superior values compared to the matrix. The systems showed a reduction on the burning rate, indicating that the flammability resistance of nanocomposites was improved.