The ex-situ method to prepare MgB superconductors is favorable in terms of bulk density compared to the in-situ method. Since the packing factor of ex-situ MgB is higher than that of in-situ MgB, a better , even higher than that of in-situ, is naturally expected if strong grain connectivity is achieved. In the present work, ex-situ MgB polycrystalline bulks with Mg addition were prepared by sintering. Combined with phase composition analysis, microstructure observation and superconducting properties measurement, it is found that Mg addition can obviously reduce MgO impurities, accelerate the self-sintering of MgB and even promote the formation of sintering necks between MgB grains. Consequently, the sintering density and grain connectivity is enhanced, and the is improved across the whole magnetic field in the ex-situ MgB sample with Mg addition. Mg addition is a promising and effective way to further enhance of ex-situ MgB superconductors.