The isothermal crystallization of poly(ethylene oxide), (PEO), single-C-60-end-capped PEO (FPEO). and double-C-60-end-capped PEO (FPEOF) has been evaluated using polarized optical microscopy (POR-I) and differential scanning calorimetry (DSC). Comparison studies were also made on a physical mixture of PEO and C-60 with the game C-60 content as in FPEO. Wide-angle X-ray diffraction experiments indicate that the crystal structures of the PEO fractions in all samples are identical. The equilibrium melting temperatures of FPEO and FPEOF are lower than that of PEG. Both the overall crystallization rate and the spherulite growth rate of C-60-end-capped PEO are markedly slower as compared to PEG, whereas there is no apparent change in the rates for PEO in the physical mixture. Kinetic analyses of the crystallization data from both DSC: and POM agree quite well. The fold surface free energy of FPEO is of about 1.8 times larger than that of PEG, while that of FPEOF is about 2.5 times larger than that of PEG. This increase in fold surface free energy has been attributed to hindrance exerted by the bulky C-60 end groups.