Abstract For investigating ring conformational requirement for the biological activity of abscisic acid, the cyclopropane analogues 6, 7, 9 , and 10 were synthesized and their biological activities in four bioassays were tested. The activity of the achiral cyclohexadienone analogue 8 also was examined. Analogue 7 in which the 6′ β-substituent is constrained essentially to the axial-like orientation between axial and bisectional showed no activity, while 6 and 8 with no axial-like substituent at C-6′β independent of the conformational preference exhibited the equivalent activity to abscisic acid. This result suggested that the axial substituent at the β-side of the ring is fatal to the activity. The active conformation of abscisic acid would be a conformation where C-9′ is equatorial and the side chain is between pseudo-axial and bisectional, that is, close to the favored half-chair with the side chain pseudo-axial rather than the less favored half-chair with the side chain pseudo-equatorial.