Five commercial barium titanate powders were subjected to various surface decontamination treatments: calcination at 500°C, followed by leaching either in pure water or acetate buffer solution. They were then de-agglomerated by ultrasonic treatment and finally characterised by XRD, TGA, XPS, EGA, pyrolysis/FT-IR, BET specific surface area and particle size analysis. The main contaminating elements in raw powders were carbon and sulphur, present as barium carbonate (between 0 7 and 1 2wt%) and barium sulphate (about 0 5 wt%). Barium sulphate is thermally stable up to 1400°C and is not affected by the treatments. Barium carbonate decomposes in two steps, between 500 and 900°C and 1200 and 1400°C by reaction with TiO 2 and BaTiO 3 to release CO 2 . Carbonation is slightly reduced by calcination, but subsequent water cleaning promotes re-carbonation. Acid cleaning substantially decreases the BaCO 3 content, down to 0 07-0 7 wt%. The remaining quantity corresponds to the most stable form which decomposes near 1200-1400°C and is still partially present at the surface of the particles. Forming of ceramics green bodies by slip casting of aqueous suspensions stabilised by ammonium poly(acrylate) was then investigated. The dispersing solution compositions have been optimised for each powder and treatment, in order to minimise the liquid/solid ratio of the slip. In all cases, the properties of the slips and of the cast specimens have been improved by the cleaning treatments: higher solid volume fractions in the slip up to 60% for the best case and higher green densities. In particular green densities as high as 70% have been obtained which is very close to the theoretical maximum packing density of log-normally polydispersed spheres. This enhancement can be ascribed to the beneficial effect of decarbonation on the deagglomeration of the powders.