Abstract: Aiming at the current ultra-wideband multiple-input multiple-output (UWB-MIMO) antenna that has a large size, low isolation, and other deficiencies, a miniaturized, high-isolation UWB-MIMO antenna is designed. The back side of the antenna is a rectangular ground plate with cutting corners, while the front side is made up of a “vase”-style radiation patch and a stepped microstrip feed line. The antenna is broad-banded by symmetrically cutting the corners of the rectangular radiating patch and etching the rectangular slot on the ground plate. The antenna achieves high isolation by loading a “fishbone” and symmetrical “Y” decoupling stubs on the front and back of the dielectric substrate. The antenna was simulated and measured with a size of only 22 mm×29 mm×0.8 mm, having an operating bandwidth of 1.5-18 GHz (the relative bandwidth reaches 169%), isolation is greater than 17 dB in the bandwidth range, and an envelope correlation coefficient (ECC) of less than 0.02. The antenna can be utilized in UWB-MIMO wireless communication systems since it has good radiation performance and a simple, small structure.