Disclosed is a method of removing metals from hydrocarbon oil, comprising: supplying a feed including hydrocarbon oil; mixing the feed with an aqueous solution including a metal scavenger to prepare a first mixture; separating the first mixture into a first aqueous solution phase and a first hydrocarbon phase and discharging the separated first aqueous solution phase; mixing the separated first hydrocarbon phase with washing water to produce a second mixture; separating the second mixture into a second aqueous solution phase and a second hydrocarbon phase; and recovering the separated second hydrocarbon phase and recirculating the separated second aqueous solution phase.