Polymer crystals of monodisperse poly (9,9-dioctylfluorene)s (PFOs, named as Fn) on mixing both components (F16 and F64) in different ratios are grown from chloroform/ethanol solutions. In these crystals, lamellar thicknesses corresponding to relevant components can be observed by utilizing atomic force microscopy (AFM). Crystallization of these polymers is accompanied by fractionated crystallization where saturation solubility of different components remarkably affects the crystallization process. Moreover, we report on the stability of the crystal under thermal annealing and solvent annealing. The crystal is thermally stable, but can be eventually dissolved at the good solvent which takes advantages of the slow crystallization process to accomplish the process. (C) 2012 Elsevier Ltd. All rights reserved.