A query tree based tag identification method in RFID systems includes: (a) forming a temporary ID for each of the tags; (b) comparing an inquiry of the reader with a portion of the temporary ID in each tag when receiving the inquiry from the reader; (c) if the inquiry and the portion of the temporary ID are identical to each other, transmitting a remainder of the temporary ID in each tag to the reader; (d) if a collision occurs in the step (c), generating new inquiries for storing them in the reader; (e) if there is no collision in the step (c), transmitting an ACK signal to each tag whose temporary ID is identified to receive its real tag ID therefrom; and (f) repeating the steps (b) to (e) until there is no inquiry in the reader.