PURPOSE: To simply and efficiently remove mercury (compound) in an oil by mixing a mercury (compound)-containing hydrocarbon oil into contact with an organic peroxide, then bringing the resultant mixture into contact with an acidic inorganic substance, extracting the obtained mixture with an aqueous solution of a polar organic solvent, and subsequently carrying out treatment with active carbon.

CONSTITUTION: (A) A mixture prepared by mixing (I) a hydrocarbon oil such as benzene, toluene, gasoline, kerosene, light oil or a natural gas condensate containing mercury and/or its compound with (II) an organic peroxide composed of preferably cumene hydroperoxide is brought into contact with (B) an acidic inorganic substance composed of a powdery or granular substance of a solid acid such as preferably acid clay, silica alumina or sulfuric acid, phosphoric acid, etc., supported thereon at normally 20-90°C (preferably 55-65°C). The resultant mixture is then subjected to extraction treatment with an aqueous solution containing a polar organic solvent such as alcohols, ketones or glycols. The aforementioned aqueous solution is subsequently brought into contact with active carbon to remove the mercury (compound) in the hydrocarbon oil.