This paper presents the effects of alkali and alkaline earth metallic (AAEM) species on the yields of products and bio-oil quality obtained from the fast pyrolysis of mallee wood. Mallee wood biomass was milled and sieved before being submitted to various pre-treatments with water or mild acid solution. After being oven-dried, the biomass was pyrolysed in a fluidized-bed reactor. AAEM contents of the pre-treated biomass samples were determined by ion chromatography. It was observed that the selected durations of water treatment did not reduce significantly the concentrations of cations present, but that the mild acid solution removed almost entirely the AAEM species from the biomass. Yields of gas and char were influenced slightly by the removal of AAEM from the biomass, while bio-oil yields were not shown to differ. Viscosity of the bio-oils increased with the removal of AAEM from the feedstock, with the greatest impact being observed with acid-washed biomass. Thermogravimetric analysis showed an increased content of oligomers in the bio-oil obtained from the acid-treated biomass, and a decrease in the lighter fractions when compared with bio-oil obtained from untreated mallee wood.