Within the binary amorphous homogeneous mixtures of conjugated polyalkylfluorene and methanofullerene, the annealing‐induced nucleation and growth of methanofullerene single crystals under the influences of molecular supply and mixing tendency have been studied in this research. As the molecular supply is satisfactory at selected annealing temperatures, the crystallization of methanofullerene is identified to advance mainly via the concurrent growth of board‐like crystals. When the diffusion is relatively limited, the local self‐aggregation of methanofullerene retards the further growth of preexistent crystals. Consequently, the successive nucleation of new single crystals on preexistent crystals emerges as the dominant mechanism of crystallization. With the advance of horizontal stacking of single crystals, the fractal‐like stacking patterns are able to evolve with long‐range continuity and facilitate the charge transportation. Nevertheless, upon the increase of annealing temperature and side‐chain length, the mixing tendency is enhanced, declining the tendency of self‐aggregation and thus successive horizontal stacking of single crystals.