The stability of ceramic suspensions can be predicted by means of zeta potential and particle size measurements but a major problem is that most existing techniques make use of diluted suspensions so that the concentrated suspensions frequently used in shape forming of ceramics are out of range. The propagation of light through a concentrated suspension can be used to characterise its colloidal stability. This work aims to study the variations of the structure of concentrated ceramic suspensions maintained at rest by multiple light scattering (MLS). This technique allows us to obtain information about the agglomeration processes that take place during ageing, like particle migration and particle aggregation. The results are compared with those obtained using conventional techniques such as the predictive tests (e.g. zeta potential and rheological behaviour of fresh suspensions) and ageing studies measured by rheometry. For such purpose, aqueous suspensions of alumina and alumina/silica (used to produce mullite by reaction sintering) have been studied.