The invention describes a process for producing P1,P4-di(uridine-5′-)tetraphosphate (U2P4) or a salt thereof from uridine 5′-monophosphate (UMP); wherein the process comprises at least one of the steps (a) and (b): (a) adding UMP diphenylphosphate (UMP-DPP) in divided portions during a step of reacting UMP-DPP with an organic alkali salt of pyrophosphate (PP1) to produce a reaction mixture; wherein at least one equivalent of a first base is present during one portion of the reaction; (b) reacting UMP-DPP with a PPi-organic alkali salt in the presence of at least one equivalent of a second base to produce a reaction mixture, wherein the first base and the second base may be the same or different; (c) subsequently adding water to the reaction mixture to produce an aqueous reaction mixture; and optionally (d) adding an alkali to the aqueous reaction mixture.