PURPOSE: To easily obtain the above compound useful as a color-developing agent for heat-sensitive recording paper, in high yield and purity, by reacting mercaptophenol with a bis(haloethoxy)methane in the presence of an alkali and a solvent and slowly cooling the obtained reaction liquid.

CONSTITUTION: 4-Mercaptophenol is made to react with a bis(haloethoxy) methane in the presence of an alkali (e.g., NaOH or KOH) and a solvent (e.g., methyl alcohol, ethylene glycol or diethylene glycol). After removing the solvent, the reaction product is added with warm water (e.g., 40W100°C, preferably 50W90°C) and slowly cooled to room temperature or thereabout at a cooling rate of 5W20°C/hr, preferably 7W15°C/hr to obtain the objective di(hydroxyphenylthio)dioxaheptane. Crystals having large particle diameter can be produced by the slow-cooling process.