PURPOSE: To obtain the titled substance useful as an intermediate for powerful herbicides against weeds which cannot be easily controlled in paddy fields, by condensing 1-methyl-5-pyrazolone with a halogen-substituted benzene, etc. in the presence of aluminum halide, and hydrolyzing the resultant condensate.

CONSTITUTION: A compound of formula I or a mineral acid salt thereof is condensed with a compound of formula II (X is halogen or alkyl, m is 1, 2 or 3) and CCl4 in the presence of an aluminum halide, and an aqueous solution of an alcohol containing a basic susbstance or an aqueous solution of a mineral acid, e.g. hydrochloric acid, is added thereto at 0W100°C to hydrolyze the resultant condensate. Thus, the aimed compound of formula III is obtained.