Abstract: The flower thinning agent of the present invention comprises a preparation of a mixture of an inorganic compound of poor water solubility with an additive, satisfying the following relationships of (a) 0.03?P?30, (b) 3?Q?800, and (c) 0.5?Q/P?1000, wherein P: average particle diameter (?m) measured by SALD-2000A laser type particle size distribution meter, Q: BET specific surface area (m2/g) measured according to the nitrogen adsorption method. The flower thinning agent of the present invention is not harmful to a human body and has not only high adaptability to the deflection of spread timing, but also high flower thinning effect.