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MgB2 is considered to be an important conductor for applications. Optimizing flux pinning in these conductors can improve their critical currents. Doping can influence flux pinning efficiency and grain connectivity, and also affect the resistivity, upper critical field and critical temperature. This study was designed to attempt the doping of MgB2 on the Mg sites with metal-diborides using high-energy ball milling. MgB2 samples were prepared by milling pre-reacted MgB2 and TaB2 powders using a Spex 8000 M mill with WC jars and balls in a nitrogen-filled glove box. The mixing concentration in (Mg1-xTax)B2 was up to x = 0.10. Samples were removed from the WC jars after milling times up to 4000 minutes and formed into pellets using cold isostatic pressing. The pellets were heat treated in a hot isostatic press (HIP) at 1000degC under a pressure of 30 kpsi for 24 hours. The influence that milling time and TaB2 addition had on the microstructure and the resulting superconducting properties of TaB2-added MgB2 is discussed. Improvement of Jc at high magnetic fields and of pinning could be obtained in milled samples with added TaB2. The sample with added 5at.%TaB2 and milled for 300 minutes showed values of Jc~ 7 times 105 A/cm2 and Fp~ 14 GN/m3 at 2 T, 4.2 K. The milled and TaB2-mixed samples showed higher values of mu0Hirr than the unmilled-unmixed sample.