Nanocomposites of a beta-nucleated propylene-ethylene random copolymer filled with different amounts of multi-walled carbon nanotubes (MWCNTs) were prepared by a melt mixing process. The complex crystalline structure that the samples exhibited was attributed to the strong alpha-nucleating effect of MWCNTs and the presence of calcium pimelate, as it was revealed by X-ray diffraction. It was found that the presence of MWCNTs at concentrations higher than 2.5 wt.% practically diminishes the effect of the beta-nucleating agent, and this was also reflected on the mechanical properties of the samples. The quality of MWCNT dispersion in the polymer matrix was evaluated by transmission electron microscopy. Mechanical and thermal properties of the nanocomposites were studied as a function of the crystalline structure and the filler content by tensile and impact testing, thermogravimetric analysis and differential scanning calorimetry. A crystallization kinetics study was also performed in order to export conclusions regarding the rates and parameters of crystallization. (C) 2014 Elsevier Ltd. All rights reserved.