The present invention relates to a process for producing a monosaccharide using a microorganism. The microorganism possesses a glycosyltransferase and a glycosidase which work together to synthesize a desired monosaccharide in free form by using an endogenous provided nucleotide activated monosaccharide, glycosylate a suitable acceptor substrate and release the desired monosaccharide by a hydrolysis reaction. The required acceptor substrate for the reaction is recycled and only needed in catalytic amounts. The monosaccharide is produced in free from and is retrieved from the supernatant of the cultivated microorganism.