C-60 and C-70 fullerene nanoparticles prepared by evaporating their powders in inert gas were investigated by electron microscopy and X-ray diffraction. Crystal structures of the particles were face centred cubic (fcc) which is a stable phase at high temperature, with lattice parameters of a = 1.42 nm for C-60 and a = 1.499 nm for C-70 Nanoparticles with definite crystal habits were sometimes observed among those with irregular ones. For the C-70 nanoparticles, the higher the source temperature was, the better-defined the crystal habits were.