PURPOSE: To enhance an adsorbing speed and to minimize non-selective adsorption to remove mercury from hydrocarbon oil by bringing a carrier with a high surface area having an adsorbent reactive with mercury supported thereon into contact with a mercury-containing hydrocarbon fluid raw material at specific temp.

CONSTITUTION: A carrier with a high surface area having an adsorbent reactive with mercury is supplied to be brought into contact with a mercury-containing hydrocarbon fluid raw material at temp. represented by formula (wherein T is temp. and BP is a b.p. wherein 90% of the hydrocarbon fluid raw material is boiled) to remove mercury present in the hydrocarbon fluid raw material. As the reactive adsorbent to be used, Au, Ag, Cu, Sn and Zn, oxides of them and sulfides of them are designated. An especially pref. combination is metal silver on alumina and CuS on SiO2/Al2O3. When the above mentioned reactive adsorbent is used, a reactive adsorbing speed is increased by a rise of reaction temp. different from physical adsorption. Not only an adsorbing speed but also adsorbing capacity are increased by high temp.