A compact CPW-fed ultra-wideband (UWB) multiple-input–multiple-output (MIMO) antenna with quad-band-notched characteristic is proposed in this work. The antenna elements are placed orthogonally, the introduction of defected ground structure (DGS) and double Y-shaped stub makes the isolation between different antenna ports better than 20 dB, and the cutting of the excess dielectric substrate part reduces the antenna area by about 30.75%. Complementary split-ring resonators and slots on the ground and the radiation patch have been introduced to achieve the four-notch characteristics at 7 GHz lower digital microwave relay communicator band, 5.8 GHz upper WLAN, 5.25 GHz lower WLAN, and 3.5 GHz WiMAX. The wide bandwidth of the antenna is obtained by applying tapered feed line and CPW feed, which covers 2.88–12 GHz with the four-notched bands of 3.34–3.93 GHz, 5.15–5.61 GHz, 5.72–6.0 GHz, and 6.75–7.6 GHz. Moreover, ECC (<0.02), DG (>9.99), the peak gain of 4.01 dB, good radiation pattern and TARC prove the presented antenna is suitable for UWB-MIMO systems.