Magnetic and conducting polypropylene (PP) polymer nanocomposites with different loadings of synthetic carbon nanotubes (CNT-Fe) were fabricated by in-situ polymerization. Chemical vapor deposition was used as the synthetic route for carbon nanotube (CNT) synthesis, in which high-surface-area silica (SiO2) acts as the support and ferrocene as the precursor and catalyst. Scanning and transmission electron microscopy analyses evidence the homogenous dispersion of the filler in the polymer matrix. It was found that, with the addition of 3.8 wt.% of the filler, the insulating PP matrix changes to a semiconductor. The magnetic properties of the nanocomposites were investigated using a vibrating sample magnetometer. The addition of 0.8 wt.% CNTs results in ferromagnetic behavior in the diamagnetic polymer matrix and high coercivities at room temperature. The thermal properties were investigated by thermogravimetric analysis and differential scanning calorimetry. Results show an increase in the maximum degradation, crystallization, and melting temperatures of the nanocomposites as compared with neat PP. (C) 2017 Elsevier Ltd. All rights reserved.