To obtain the subject compound that is useful as a pharmaceutical, agrochemical and other chemicals in high yield by reaction of a specific unsaturated ketone with a nucleophilic agent in the presence of a quaternary ammonium salt in an aqueous solvent.

The reaction of (A) an α, β-unsaturated ketone of formula I (R1 and R2 are each H, a halogen or the like) as (3-(p-methoxyphenyl)-1- phenyl-2-propen-1-one with (B) a nucleophilic agent of the formula: NuH (Nu is a nucleorphilic substituent) as thiophenol is carried out in the presence of (C) a quaternary ammonium salt as trimethyl hexadecylammonium chloride in an aqueous solvent at 20-50°C where the amount of the component B is 0.5-2 moles of the component B per mole of the component A and the component C is 1-10 mol.% based on the component A to give the objective β-substituted ketone as 3-phenylthio-3-(p-metoxypheny1)-1-phenyl-1-propanone.