A method purifies 1-aminocyclopropanecarboxylic acid by subjecting a crude 1-aminocyclopropanecarboxylic acid to crystallization with a solvent mixture containing an organic acid having one to five carbon atoms and a poor solvent for 1-aminocyclopropanecarboxylic acid, which poor solvent is miscible with the organic acid. In the method, the solvent mixture may further contain water. Purification may be carried out by mixing the crude 1-aminocyclopropanecarboxylic acid with the organic acid having one to five carbon atoms, removing insoluble matter by filtration, and adding the poor solvent with or without water to the filtrate to thereby crystallize 1-aminocyclopropanecarboxylic acid.