The hydrogen-bonding strength of poly(epsilon -caprolactone) (PCL) blends with three different well-known hydrogen-bonding donor polymers [i.e., phenolic, poly(vinyl-phenol) (PVPh), and phenoxy] was investigated with differential scanning calorimetry and Fourier transform infrared spectroscopy. All blends exhibited a single glass-transition temperature with differential scanning calorimetry, which is characteristic of a miscible system. The strength of interassociation depended on the hydrogen-bonding donor group in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL, which corresponds to the q value of the Kwei equation. Tn addition, the interaction energy density parameter calculated from the melting depression of PCL with the Nishi-Wang equation resulted in a similar trend in terms of the hydrogen-bonding strength. Quantitative analyses on the fraction of hydrogen-bonded carbonyl groups in tile molten state were made with Fourier transform infrared spectroscopy for all systems, and good correlations between thermal behaviors and infrared results were observed.