Carbon nanotube-alumina hybrid reinforced high density polyethylene (HDPE) matrix composites were prepared by melt processing technique. Microstructure studies verified that the nanotubes consisting of well-crystallized graphite formed a network structure with Al2O3 in the hybrid, which was homogeneously dispersed in the HDPE matrix composites. Mechanical measurements revealed that 5% addition of nanotube-alumina hybrid results in 100.8% and 65.7% simultaneous increases in Young's modulus and tensile strength, respectively. Fracture surface showed homogenous dispersion of nanotubes and Al2O3 in the HDPE matrix and presence of interlocking like phenomena between hybrid and HDPE matrix, which might contribute to the effective reinforcement of the HDPE composites. (C) 2011 Elsevier Ltd. All rights reserved.