[Problem] To provide a method for easily and stably storing P1, P4-bis(5'-uridyl)tetraphosphate crystals for a long period of time. [Solution] A method for storing P1, P4-bis(5'-uridyl)tetraphosphate crystals or a pharmaceutically acceptable salt thereof in a package, which is characterized by storing under one condition selected from among the storage conditions (1)-(3) described below. (1) The storage temperature is 0oC or higher but lower than 25oC. (2) The storage temperature is 25oC or higher but lower than 40oC, and the crystal pH is 4.5-8.0. (3) The storage temperature is 40oC or higher but lower than 60oC, and the crystal pH is 5.0-6.4.
