The interaction between erythritol and 4-hexylresorcinol during heating was investigated by thermal analysis, powder X-ray diffractometry and infrared spectroscopy. A phase diagram was constructed by measuring the thermal behaviour of various resolidified physical mixtures of erythritol and 4-hexylresorcinol. The phase diagram revealed complex formation between erythritol and 4-hexylresorcinol with incongruent melting at 84C; the stoichiometry was a molar raio of 1:2 erythritol:4-hexylresorcinol. The complex gave diffraction peaks at 2θ=5.6 and 11.2 in the X-ray powder diffraction pattern. In the infrared spectrum, a new peak due to the complex was observed at 3504 cm–1. The complex prepared by grinding and evaporation had the same molecular arrangement as the complex prepared by sealed heating.