A di(pyrimidine nucleoside 5′-)polyphosphate is synthesized by converting a pyrimidine nucleoside 5′-triphosphate into a pyrimidine nucleoside 5′-cyclic triphosphate by use of a condensing agent, and subsequently reacting the pyrimidine nucleoside 5′-cyclic triphosphate with a pyrimidine nucleotide in the presence of a salt of a metal selected from among magnesium, manganese, and iron.Through the method of the invention, a di(pyrimidine nucleoside 5′-)polyphosphate can be synthesized from an unprotected pyrimidine nucleoside 5′-phosphate serving as a starting material at a synthesis yield of 50% or higher. Therefore, the method of the invention is suitable for large-scale synthesis of a di(pyrimidine nucleoside 5′-)polyphosphate.
