The morphological, mechanical, thermal, and tribological properties of high-density polyethylene (HDPE) composites reinforced with organo-modified nanoclay (3 and 6 wt%) were studied. A commercial maleic anhydride-based polymeric compatibilizer (PEgMA) was used to improve the adhesion between the polyethylene and clay. Transmission electron microscopy (TEM) characterization of composites revealed that nanoclay exists mainly in a multilayered structure in the HDPE matrix. Mechanical testing of composites showed that Young's modulus and tensile strength increased with nanoclay content. Coefficients of the linear thermal expansion (CLTE) of HDPEPEgMAclay composites were slightly lower in the flow direction than those of HDPEPEgMA. The tribological properties were measured in dry conditions against a steel counterface. The friction coefficient of the matrix was decreased by the addition of clay. Electron microscopic results suggested that the wear mechanism for HDPE and HDPE composites was mainly adhesive. Clay agglomerates were observed on the worn surfaces of the composites, which may partly explain decreased friction. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers