A method for determining a three-dimensional position of an RFID tag includes moving a mobile object carrying an RFID antenna in a workplace to a first position where the RFID antenna receives a radio signal from the RFID tag. A horizontal angle and a vertical angle are determined from the RFID antenna to the RFID tag based on the feasibility of communication between the RFID antenna and the RFID tag as the RFID antenna is turned or moved in a horizontal direction and a vertical direction, respectively, at the first position. A distance from the RFID antenna to the RFID tag is determined based on the power of the signal received from the RFID tag. A three-dimensional position of the RFID tag is determined by vector calculation using the horizontal angle, the vertical angle, and the distance.