PURPOSE: To obtain diglycerol in high yield and purity in a simple apparatus with little energy without coloring, etc., by flash evaporating a mixture containing the diglycerol under reduced pressure in one stage, and partially condensing the resultant diglycerol at a specific temperature.

CONSTITUTION: Diglycerol is separated and purified from its mixture with glycerol, triglycerol, tetraglycerol and further a higher polyglycerol, etc. In the process, the mixture is flash evaporated at a reduced pressure of 10 Torr of less, and then partially condensed in a temperature range of the dew point of the diglycerol at the corresponding vapor pressure 100°C lower than the dew point, e.g. 120W220°C, preferbly 120W170°C at 5 Torr, to give the diglycerol as a condensate.