The results are presented of a research into technological possibilities of controlling the transgalactosylation process of lactose, catalyzed by the commercially available β-galacosidases, in a permeate obtained after the ultrafiltration of whey, in order to improve the efficiency of GOS and/or of lactulose synthesis. It was proved that the selected β-galactosidase and the substrate concentration decided on the efficiency of synthesis, and, in the case of the synthesis of lactulose, the ratio of lactose and fructose amounts as added to the reaction mixture. The efficiency of GOS synthesis and, first of all, of lactulose (65 % m/V in total saccharides) is found acceptable. A favourable content of GOS, i.e. 13.7 %, in saccharides was recorded after the process run in a solution of permeate with 10 % (m/V) of lactose using Ha-Lactaseto catalyze the reaction. Based on the research conducted, a special technology of GOS and/or lactulose synthesis is suggested with a permeate after the ultrafiltration of milk or whey applied (as a source of lactose). The obtained concentrates of GOS can be applied as a source of prebiotics in the production of health promoting food, feedstuffs or pharmaceuticals. The postulated technology provides an opportunity for attractive, waste-free management of permeates after the ultrafiltration of milk or whey. The subsequent investigations in this field will address experiments aiming at evaluating the conditions of continuous synthesis of GOS and/or lactulose with the use of immobilized enzymes.