The equivolumetric ZrO2-Al2O3 ceramic composite shows very good mechanical properties due to its interpenetrating microstructure; unfortunately it is very difficult to achieve a well dispersed aggregates＇ free mixture. In this paper ultrasonication was used as a dispersion and mixing aid for aqueous suspension of ZrO2-Al2O3 powders. The suspensions were stabilised using either an electrostatic or an electrosteric mechanism. The influence of ultrasonication time as well as solid contents in the suspensions were investigated via rheological measurements. The goal was to optimise the process in order to obtain a well dispersed system without aggregates. The results indicate that there is, for every system, a threshold time over which aggregates start to reappear.