| abstract |
A crystal of free acid of 3′,5′-cyclic diguanylic acid containing no metal salt with cobalt, magnesium or the like is provided. A method is sought for obtaining said crystal in a large amount and with ease. By a manufacturing method comprising a step of adding acid to an aqueous solution of 3′,5′-cyclic diguanylic acid so as to lower pH to 1 to 3, crystals of 3′,5′-cyclic diguanylic acid can be obtained in a large amount with ease. Said crystals are free acid crystals which do not contain a metal salt with cobalt, magnesium or the like. |