A crystallization-based process that separates pure fullerenes C-60 and C-70 from their mixture using o-xylene as the solvent has been developed. Isothermal solid liquid equilibrium phase diagrams of the C-60-C-70-o-xylene ternary system for a number of temperatures were first determined at 1 atm. Taking advantage of the shift in solvent-free composition of the C-60-C-70 double saturation point with temperature and based on the solid solution-forming phase behavior between C-60 and C-70, the flowsheet of a general crystallization process was then synthesized. It involved the fractionation of a C-60-C-70 fullerene mixture into C-60-rich and C-70-rich solid solutions using temperature-swing crystallization, followed by purification of the solid solutions with multistage crystallization into pure C-60 and C-70 solids. To demonstrate process feasibility, bench-scale batch experiments were performed using a commercially available fullerene mixture that was pretreated by adsorption to remove higher fullerenes. C-60 and C-70 solids of purity higher than 99 wt % were obtained. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 1801-1812, 2010