[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.
