Abstract: A method is described for the preparation of lactulose by isomerizing lactose to lactulose, followed by complexing lactulose to boric acid. The isomerization reaction is carried out in alkaline solution, and it is followed by splitting the lactulose-borate complex in acidic solution and separating the two components. Separation is achieved by crystallizing boric acid, filtering the crystals out of the product mixture, evaporating the product mixture to form a concentrate, recirculating the concentrate to the crystallization step where it is mixed with fresh reaction mixture in order to provide volume and nuclei for the crystallization of the boric acid in the reaction mixture, then passing the resulting mixture through another filtration step followed by an additional separation step by column chromatography.