Small-angle X-ray scattering and differential scanning calorimetry were used to study the morphology in segmented polyester-based polyurethanes with 4,4＇-methylene bis(phenyl isocyanate) and butanediol as hard segment. The polyesters with various mole ratios of -CH3 side chain were synthesized from adipic acid and glycols which were mixtures of various mole ratios of hexanediol and 1,2-propanediol. The effect of -CH3 sidechain content in polyesters on the phase segregation of soft-and hard-segments of polyurethanes at two annealing temperatures, i.e. 25 and 87 degrees C, was observed.