[Problem] Provided is a method for easily and stably storing crystals of P1,P4-bis(5'-uridyl)tetraphosphate for a long term.[Solution] A method for storing packed crystals of P1,P4-bis(5'-uridyl)tetraphosphate or a pharmaceutically acceptable salt thereof, wherein one of the following storage conditions (1) to (3): (1) a storage temperature of 0°C or more and less than 25°C； (2) a storage temperature of 25°C or more and less than 40°C and a crystal pH of 4.5 to 8.0； and (3) a storage temperature of 40°C or more and less than 60°C and a crystal pH of 5.0 to 6.4 is selected and the crystals of P1,P4-bis(5'-uridyl)tetraphosphate or the pharmaceutically acceptable salt thereof are stored under the selected condition.
