(S)-(+)-3′-Fluoroabscisic acid (5a) was synthesized as an analogue of abscisic acid that can resist the metabolic cyclization of 8′-hydroxyabscisic acid to phaseic acid due to increased electron density at C-2′. The inhibitory activity of 5a was slightly higher than that of abscisic acid in lettuce seed germination, and was almost equal to that of abscisic acid in rice seedling elongation. When 5a