The effects of powder loading and binder additive on the theology, moulding, and sintered properties of alumina injection-moulding blends were studied. The melt viscosity increased with the powder loading, which enhanced the defect concentration of the moulded parts when the powder loading was higher than 0.54 volume fraction. This transitional powder loading was much smaller than the critical powder loading of 0.65 derived by fitting the theological data with a mathematical model. The low molecular weight acidic binder additives used in this study effectively reduced the melt viscosity. However, additives that yielded a large quantity of burn-out residue deteriorated the sintered properties. A high powder-loading mixture having a low melt viscosity and good powder dispersion was achieved by eliminating powder agglomerates before mixing, and by using an appropriate binder additive.