PURPOSE: To collect 1,4-naphthoquinone efficiently in bringing a formed hot gas obtained by catalytic vapor phase oxidation of naphthalene with molecular oxygen-containing gas, by suppressing remarkable foaming by the use of a Venturi scrubber.

CONSTITUTION: In collecting 1,4-naphthoquinone useful as a raw material for dye, etc., by bringing a formed hot gas containing 1,4-naphthoquinone obtained by catalytic vapor phase oxidation of naphthalene with molecular oxygen- containing gas, phthalic anhydride and an unreacted raw material into contact with water, the contact of the formed hot gas and water is carried out by a Venturi scrubber 1 to collect the aimed compound in high collection efficiency without causing remarkable foaming. Since an ordinarily useful Venturi scrubber can be utilized,the method is simply performed and operating conditions can be readily controlled. Further there is no demerits such as danger followed by use of organic solvent, bad influence on environment, cost, etc.