A process for the preparation of a 2-chloro-2-deoxy-mono-, di- or oligo-saccharide comprises reaction of a mono-, di- or oligo-saccharide derivative having a free hydroxy group in at least 2- position and having the hydroxy group in at least the 1- and 3- positions protected from chlorination, with sulphuryl chloride in the presence of an organic base in a chlorinated hydrocarbon solvent at a temperature below -40.degree. C. to form a chlorosulphate derivative with a chlorosulphate group in at least the 2-position, which chlorosulphate derivative is then reacted with lithium chloride in the presence of hexamethylphosphoric triamide to replace chlorosulphate groups with chlorine atoms to form a chlorodeoxy derivative, which chlorodeoxy derivative is then freed of unwanted protecting groups.