Activated anionic ring-opening polymerization of epsilon-caprolactam (ECL) was carried out for the first time in the presence of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) to prepare polyamide 6 (PA6)-based composites comprising up to 3 wt% of this fullerene derivative. This in situ polymerization process produced high molecular weight composites containing 52-80 % of gel fraction at PCBM concentration a parts per thousand yen0.5 wt%. Spectral, thermo-mechanical, synchrotron X-ray, and scanning electron microscopy data were used to elucidate the structure and morphology of the PA6/PCBM composites. A mechanism of the chemical structure evolution was proposed starting with incipient complexation between ECL and PCBM, via subsequent chemical linking of ECL moieties on the C-60 spheroid and final formation of star-burst and cross-linked morphologies. PCBM amounts of 0.1 wt% and more decreased the volume resistivity from 10(12) Omega cm (neat PA6) to 10(9)-10(7) Omega cm, thus opening the way for new applications of anionic PA6.