A compact six elements MIMO antenna is presented for UWB applications. The proposed MIMO array consists of non-identical monopole antennas with distinctive ground planes so as to nullify mutual coupling amid side-by-side elements. Also, by properly placing the antenna elements exploiting cross polarization diversity, a good isolation throughout the operating bandwidth is achieved. Moreover, two parasitic inverted L stubs in combination with small rectangular stubs are employed near the middle-placed radiators and corner placed radiators, respectively, in order to extend the frequency band and enhance the impedance matching. Results show a good reflection coefficient about -10 dB, a high isolation >20 dB, an envelope correlation coefficients <0.15, a high diversity gain equal to 9.3, and finally, a maximum value of efficiency for both used antenna elements which is about 78% and 60% with 6 and 5 dBi of gain, respectively. They validate the proposed MIMO antenna efficiency for UWB diversity applications.