Abstract: The present invention aims at providing a convenient method of producing zinc pyrrolidonecarboxylate dihydrate, which is an industrially useful compound, with high optical purity, a higher yield, and better dissolution property. The present invention also provides a convenient method of producing zinc pyrrolidonecarboxylate dihydrate with higher optical purity, a higher yield, and better solution property by adding a zinc salt to an aqueous medium containing a salt of pyrrolidonecarboxylic acid as a starting material and separating a crystal from the aqueous medium at a specific pH.

Abstract: Herein is disclosed a liquid composition containing a specific amide group-containing guanidine derivative or/and a salt thereof (component A) and at least one (component B) selected from the group consisting of an inorganic salt, an organic acid salt, a nonionic surfactant and an ampholytic surfactant with an action to suppress the generation of the precipitate of the component A, in accordance with which can be provided a method for suppressing the generation of the precipitate of a specific amide group-containing guanidine derivative or/and a salt thereof in a liquid composition containing the derivative or/and a salt thereof, as well as such liquid composition with improved storage stability can be provided.