Abstract This paper presents a new method of testing Delta Radar Cross Section (RCS) of Ultra High Frequency Radio Frequency IDentification (UHF RFID) tag using Giga-hertz Transverse ElectroMagnetic (GTEM) cell. Through the theoretical analysis of RFID tag’s equivalent circuit and its scattering characteristics, the paper demonstrates that the Delta RCS of UHF RFID tag tested in GTEM cell is consist with that tested in free space. Also, the contrast experiments in GTEM cell and anechoic chamber are taken to validate the feasibility and practicability of using GTEM cell to do the Delta RCS test of passive RFID tag.