This letter proposes a wideband absorber using a multiresonant gridded-square frequency-selected surface structure. Equivalent circuit models of parallel LC resonant circuits in series are given to clarify the multiresonant working principle. Using this method, a quad-resonant absorbing ground plane is designed. Surface current distributions are shown to explicate the multiresonant modes. By using the proposed absorbing ground, a wideband dipole's radar cross section (RCS) can be reduced effectively. Measured results show that 50% absorption bandwidth of the proposed absorbing ground plane is from 2 to 2.7 GHz, and maximum RCS reduction of the antenna with absorbing ground is 5 dB. The peak gain of the antenna still maintains above 6.8 dBi in the frequency range from 1.66 to 2.76 GHz. The proposed absorbing ground has advantages such as multiresonant mechanism, wideband absorbing bandwidth, and polarization independence. Thus, it can be used to reduce antenna's RCS with maintained radiation performance.