Abstract: Carbon nanotube (CNT)/high-density polyethylene (HDPE) composites with different CNT fractions were prepared by melting the blend, and the mechanical properties and crystallization of the CNT/HDPE composites-obtained were investigated. It was found that the tensile modulus of the CNT/HDPE composites with 2 w/%, 5w/% and 10w/% CNTs are increased by 7.4%, 27.0% and 28.6%, respectively, and the yield strength is increased by 3.3%, 14.4% and 18.5%, respectively, but their strength and elongation at fracture are decreased. The differential scanning calorimetry (DSC) results show that the onset temperature of crystallization (T0) of HDPE is increased and the activation energy of crystallization is decreased due to the presence of CNTs, but its crystallization rate and crystallinity are decreased due to the hindering of the movement of the HDPE molecular chains by CNTs during crystallization.