Understanding YSZ powder behaviour in different processing conditions such as calcination and subsequent milling is crucial in developing the dense and porous microstructures required for fuel cell applications. In this research, as received and calcined Tosoh YSZ (ZrO2 stabilised with 8 mol% Y2O3) was milled in water and characterised by SEM, TEM, XRD, light-scattering particle size. BET, zeta potential and acid-base titration. It is found that YSZ crystals and particles enlarge with increasing calcination temperature and as expected, shrink following milling. Calcination-milling leads to formation of particles with higher surface charge and shifts the isoelectric point (IEP) towards lower pH values. YSZ suspensions show a high viscosity and larger agglomerates at basic pHs which lead to significant porosity formation. This is despite the high zeta potential of the suspension and is attributed to increased hydrogen bonding which causes strong particle agglomeration. While acidic YSZ slips are suitable for slip casting, the basic YSZ slips are potential compositions for gel casting. Acid-base titration results indicate a direct relationship between powder surface area and the amount of acid/base used for pH adjustment. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.