PURPOSE: To simply obtain a phenyl ketone useful as a synthetic intermediate for medicines, agrochemicals, chemicals, etc., in a high yield by reacting a metyl-substituted phenyl ketone with bromine and then adding and reacting water therewith.

CONSTITUTION: A compound of formula I (R1 is F, Cl, Br, methyl, methoxy, etc.; R2 and R3 are each H, F, Cl, Br, trifluoromethyl, etc.; R1 and R2 are each methylenedioxy formed by binding) is reacted with bromine at 30-45°C. Water in an amount of 0.5-2.5 times (weight ratio) of the compound of formula I is then added and reacted therewith at 30-45°C to afford a compound of formula II. The bromine is used at 0.8-0.99 molar ratio to the compound of formula I. The compound of formula II is useful as an intermediate for medicines such as a therapeutic agent for diabetes or hyperglycemia or a preventing and a therapeutic agents for obesity.