Summary: The hydrogen bonding and phase behaviour of blends of poly(vinylphenol-co-methylmethacrylate) (PVPhMMA50) containing 50% of methyl methacrylate with poly(vinylmethylketone) (PVMK) were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). It was shown that all the blends have a single glass transition over the entire composition range. The FTIR study reveals the presence of intermolecular hydrogen-bonding interactions occurring between hydroxyl and carbonyl groups of vinylphenol (PVPh) and (PVMK) and intensified when the amount of PVMK increased in blend. A new band characterizing these interactions at 1713 cm−1 was observed. Furthermore, the quantitative FTIR study carried out for PVPhMMA50/PVMK blends was also performed for the vinylphenol and vinylmethylketone functional groups.