Glass substrate has superior shock resistance and higher stiffness for increased rpm and access time than Al/NiP substrate. The main barrier for the use of glass instead of Al/NiP in desktop computers has been the high cost of the glass substrate, which is mostly caused by its need for a long polishing time. Developing a glass CMP slurry that can deliver a higher polishing rate and fewer surface defects is a continuous challenge in the disk industry. We recently discovered that adding montmorillonite particles into a ceria-based glass CMP slurry can significantly increase the polishing rate without sacrificing the surface smoothness. It is the first time, to our knowledge, that this strong synergistic effect between ceria and montmorillonite particles was reported in the glass CMP area. Several physical properties of the ceria- montmorillonite slurries, such as viscosity, zeta potential, and particle size, are characterized in order to understand the mechanism of the synergistic effect.