Abstract: An anti-interference rectangular waveguide slot array antenna is presented in this paper. The anti-interference performance of the antenna is improved by periodically loading a row of T-shaped resonators at the bottom broad wall of the rectangular waveguide. A four-slot rectangular waveguide slot array antenna based on T-shaped resonators is simulated, designed and fabricated. The measured results show that the impedance bandwidth is 10.3% (5.5−6.1 GHz) with realized gains of 11.5−12.8 dBi and antenna efficiency of 72.1%−87.3%. Compared with a traditional rectangular waveguide slot array antenna, the anti-interference ability of the proposed antenna is improved by 32.2−69.3 dB in the suppression band of 7.9−9.6 GHz, so it is suitable for multi-band and multi-task wireless communication and radar systems.