The isothermal crystallization kinetics, semi-crystalline morphology and thermal behavior of poly(ethylene oxide) (PEO) in miscible binary blends with an amorphous component, poly(ether sulphone) (PES), were investigated below LCST by means of optical microscopy, differential scanning calorimetry and small angle X-ray scattering. Addition of PES to PEO reduces both the overall crystallization rate and the spherulite growth rate of PEG. The change of the nucleation regime and an Avrami analysis of the crystallization kinetics are discussed. The double melting behavior of PEO in blends with PES is attributed to both secondary crystallization and recrystallization during heating. A change in the supermolecular structure from intermediate spherulite-hedrite to spherulite appears on blending PEO with PES. The segregation behavior of amorphous PES during crystallization of PEO is investigated. (C) 1999 Elsevier Science Ltd. All rights reserved.