The present invention is directed to, for example, an oligosaccharide having at an end thereof a 4-position halogenated galactose residue represented by formula (I): ##STR00001## (wherein X represents a halogen atom, and R represents a monosaccharide, an oligosaccharide, or a carrier), a transferase inhibitor containing the oligosaccharide, and a method for inhibiting sugar chain elongation reaction in the presence of glycosyltransferase, the method including employing the inhibitor. The invention also provides a method for producing a 4-position halogenated galactose sugar nucleotide represented by formula (II): ##STR00002## (wherein each of R.sub.1 to R.sub.3 represents a hydroxyl group, an acetyl group, a halogen atom, or a hydrogen atom; X represents a halogen atom; and M represents a hydrogen ion or a metal ion), wherein the method employs bacterium-derived galactokinase and bacterium-derived hexose-1-phosphate uridylyltransferase. The invention is also directed to a sugar chain containing 4-position halogenated galactose envisaged to be employed as drugs and other materials, and to applications of the compound.