A combined experimental and theoretical investigation of the sedimentation of unstable colloidal ceramic suspensions has been performed. Suspensions containing submicron-sized alpha - Al2O3 particles were prepared at various pH values in order to modify suspension stability. Particle volume fraction during sedimentation was determined as a function of position and time by gamma-ray densitometry. A population balance model was developed to account for various coagulation and decoagulation mechanisms that affect sedimentation behavior in flocculating suspensions. Model predictions were then compared with experimental measurements, in order to establish the validity of the theoretical model.