The dynamic backscattering analysis of impedance loaded wire antennas for passive RFID applications is presented where the two loading impedances represent the corresponding logic states in the transmitting data of RFID tags. The analysis is based on the equivalent circuit of receiving antennas from moment method and the time-varying load calculation from the conversion matrix technique in the frequency domain. Simulation studies on 915MHz with resistive or capacitive loads are shown where the reactive load indicates more apparent discrimination for the two logic states, thereby improving the receiving sensitivity of RFID readers. The analysis methods and results can provide useful information for antenna and IC designs of RFID tags.