PURPOSE: To produce a brominated diol useful as an excellent flame-retardant, in high purity and selectivity, by reacting brominated bisphenol A or brominated bisphenol S in the form of slurry in an alkylene oxide in the presence of a catalyst.

CONSTITUTION: A brominated bisphenol A or brominated bisphenol S (preferably tetrabromide) is slurried with an alkylene oxide (preferably ethylene oxide or propylene oxide), and is reacted in the presence of a catalyst (preferably a tert-amine, especially diethanol butylamine) to obtain a brominated diol composed of 2mol of alkylene oxide added to 1mol of the brominated bisphenol.

EFFECT: The objective compound can be produced economically, in short step at a low temperature without using a solvent.

USE: Flame retardant for polyurethane, polyester and various other plastics, synthetic fibers, etc.