By means of ill situ small-angle X-ray scattering/wide-angle X-ray scattering/differential scanning calorimetry (SAXS/WAXS/DSC), structural evolution of poly(9.9-di-n-octly-2,7-fluorene) (PFO) in a cold crystallization process was quantitatively examined. After removal of background scattering from the fractal-like structure, SAXS profiles obtained during programmed heating of ail amorphous PFO specimen unveil a sequence of stages of structural evolution. These include (1) a frozen-in stage below the,lass transition temperature (T-g approximate to 62 degrees C) (2) the nucleation of prolate nano-rains with radius of gyration R-g approximate to 3.3 nm from 65 to 85 degrees C, (3) growth of the prolate ellipsoids LIP to R-g approximate to 5.0 nm between 95 and 105 degrees C. and (4) coalescence (and thickening) of the nanocrystals into oblates (of R-g approximate to 10 nm) upon further heating to 145 degrees C. There were no further changes in morphologoical features in the subsequent isothermal annealing at 145 degrees C for LIP to I h. as the size of the coalesced nanograins quickly reached a threshold value where the orientation and attachment of neighboring nanograins via thermally activated Brownian rotation became seriously hindered. Developments in the DSC-determined crystallinity (X-c,X-DSC) and the degree of heterogeneity (Q(inv) from SAXS) coincided with the nucleation and growth stages. respectively; in contrast, buildup of the WAXS-determined crystallinity (X-c,X-WAXS) proceeded mainly in the Subsequent coalescence stage where large nanocrystallites were developed.