Polyester-based polyurethanes containing approximate to 60 wt % of polyester were synthesized from low molecular weight polyester (M-n approximate to 2000) and 4,4'-methylene bis(phenyl isocyanate) (MDI), with butanediol as a chain extender and glycerol as a crosslinker. The triol crosslinker was used in substitution for the 1,4-butanediol chain extender; thus, the crosslinker was chemical bonded to the hard segments of polyurethane. The morphologies of these polyurethanes were studied by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), TMA (thermal mechanical analysis), and FTIR (Fourier transform infrared spectroscopy). Owing to the highly steric hindrance, the presence of triol crosslinker in the hard segments resulted in a decrease in the aggregation of hard segments through hydrogen bonding. The experimental results revealed that the degree of phase segregation of soft and hard segments decreased with increasing the triol crosslinker content in the hard segments.