PURPOSE: To carry out efficient isolation of abscisic acid in a high yield from a dilute solution containing abscisic acid using a reduced amount of the solvent.

CONSTITUTION: The isolation process for abscisic acid comprises the extraction step of bringing the aqueous abscisic acid into contact with an organic solvent immiscible with water to transfer the abscisic acid into the organic solvent, the concentration step of concentrating the separated organic layer containing abscisic acid into abscisic acid and the organic solvent, the recycling step of recycling the organic layer separated in the concentration step to the extraction step, and the isolation step of crystallizing out abscisic acid from the concentrated solution. The isolated abscisic acid lowers the purification load thereafter to give ABA of high purity inexpensively in an industrial scale.