Nanoparticles of C60 and C70 prepared by aerosol flow reactor method show a well developed morphology when produced at sufficiently high temperatures. Hexagonal plate shaped, icosahedral and decagonal particles of C60 and C70 are formed. Morphology and internal structure are studied by scanning and transmission electron microscopy. The plate-like particles are lamellar–twinned and grow preferentially on the side-faces by nucleation of new molecular layers along re-entrant corners. The decagonal multiply twinned nanoparticles are strained and show a distinct deviation from cubic symmetry. Some of the C70 particles exhibit a modulated structure to accommodate the internal stress; this is possible because of the ellipsoidal shape of the C70 molecule.