In this paper, the preparation of mullite suspension for electrophoretic deposition (EPD) is presented. It shows that the successful deposition of mullite coating is closely related to the weight ratio of mullite powder to ethanol solvent, and the concentration of phosphate ester (PE) in ethanol solvent, which is employed to positively charge the mullite particles in suspension. The polyvinyl butyral (PVB) is necessary as binder in the suspension. With increasing the powder:ethanol weight ratio, the content for the PVB in the suspension will also increase in order to make the deposited layer adhere to the substrate. The compositions of the mullite suspension were optimized and the process was determined based on the surface quality. It provides a new route to develop mullite coating on SiC or Si3N4 ceramic materials for high temperature application.