Metal injection moulding (MIM) is a versatile technology used for the mass production of small metallic parts with complex geometry. MIM makes use of highly-filled polymers with metal particles that can be sintered after the polymer is removed to obtain a solid metallic part. The polymeric components of the MIM feedstock serve as a processing aid to transport and shape the metallic particles in an injection moulding machine. Thus, the rheological behaviour of MIM feedstocks is critical to ensure the quality of the produced parts by the MIM process. There are many factors that affect the rheology of MIM feedstocks, including the binder composition, amount of filler particles, particle size and shape, and as it is shown in this study the chemical composition of the filler particles. Particles with a comparable size distribution of steel, titanium and aluminium were introduced into a fixed binder system at 30, 45 and 60 vol% concentrations. Small amplitude oscillatory tests were performed on all of the materials at a constant temperature. It was observed that depending on the chemical nature of the particle the magnitude of the rheological properties (complex viscosity, storage and loss moduli) were affected differently as the powder content increased from 30, 45 to 60 vol% for the different metallic alloys.