Ultrafine grained WC cemented carbides were manufactured successfully by reaction sintering with Co-Al intermetallic compounds as binder from mixed powders of a nominal composition of WC-8Co-2Al (wt%). The purpose of adding aluminum to the composition is to promote the mechanical properties of hardmetals by the in situ formation of Co-Al intermetallic phase. To manufacture bulk ultrafine WC hardmetals, ultrafine and even nanocrystalline WC powders were prepared as precursors from the mixed commercial powders by mechanical milling. Experimental results show that the transverse rupture strength and hardness of sintered hardmetal reached the maxima, being 1747.8 MPa and 90.2 HRA respectively, when the milling time expands to 55 h. It is affirmed that mechanical milling weakens the thermostability of WC-8Co-2Al powders, and facilitates the formation of Co-Al intermetallic compounds. However, overlong milling results in decreasing of properties and densities of sintered hardmetals, because the powder particles are severely refined and markedly agglomerated.