In this paper, a UWB MIMO antenna for an on-body application is proposed and antenna performance with body effect and the impact on the human body are investigated. The proposed MIMO antenna is composed of an UWB antenna above ground plane and an additional isolator located between the two antennas to enhance the isolation characteristic. A Simulation is performed to analyze the effect of the human body on the antenna performance when the human body is located near the antenna. According to the simulated result, the diversity performance of the proposed antenna is good since the Envelope Correlation Coefficient(ECC) remains below 0.1 over the UWB lower band. The simulated SAR value of antenna is 0.92 W/kg, when 1 mW input power is engaged. This value satisfies the FCC guideline which states that the 1-g average SAR should be lower than 1.6 W/kg.