Single crystal X-ray diffraction and IR spectroscopy have been used to study the conformation of 2-hydroxyphenyl 2-hydroxy-2-(α-naphthyl)vinyl ketone in solid state. It was found that one of the two possible enol tautomeric forms is stabilized in the crystal. The 1-hydroxy-3-oxo-1,3-propenylene moiety, O=C—CH=C—OH, shows a strong intramolecular H bond with a definite character of reasonance-assisted hydrogen bond in spite of being in competition with ring intermolecular hydrogen bonds. The comparison of the present results with solution NMR data indicates that the molecular geometry in solid state and in solution are similar.Facultad de Ciencias Exactas