PURPOSE: To obtain a cotylenol derivative having excellent plant growth regulation activity.

CONSTITUTION: The cotylenol derivative is a compound expressed by formula I (Me is methyl). The compound is produced by reacting a ketone compound of formula II with a reducing agent (e.g. NaBH(OCOCH3)3) in a solvent (e.g. THF) at -20 to +40°C for 1-24hr, optionally treating the reaction liquid with a dilute alkaline water such as NaHCO3 solution after the reaction, subjecting to extraction with organic solvent, concentration, etc., and optionally purifying by silica gel chromatography, recrystallization, etc. The amount of the reducing agent is 2-4mol based on 1mol of the ketone compound of formula II. The compound of formula II can be produced from the compound of formula III via 17 steps.