The invention relates to a continuously operated process for the purification by distillation of the 1,2-propylene glycol formed as by-product in the synthesis of propylene oxide, wherein the mixture formed in the synthesis which contains the 1,2-propylene glycol is separated in a dividing wall column into low-, intermediate- and high-boiling fractions and the 1,2-propylene glycol is taken off as intermediate boiler at the side offtake of the column.