Activated anionic ring-opening polymerization of e-caprolactam (ECL) was carried out for the first time in the presence of [6,6]-phenyl-C61-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 C0.5 wt%. Spectral, thermomechanical, 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 C60 spheroid and final formation of star-burst and cross-linked morphologies. PCBM amounts of 0.1 wt% and more decreased the volume resistivity from 10E12 ??.cm (neat PA6) to 10E9???10E7 ??.cm, thus opening the way for new applications of anionic PA6. ; Funda????o para a Ci??ncia e a Tecnologia (FCT)