The relationship between the abrasive particle size and the chemical mechanical planarization (CMP) performance has been investigated. The polishing rate of a Ceria slurry in CMP of a plasma enhanced tetraethylorthosilicate (PETEOS) film was examined to envisage the effect of the agglomerated particle size on the polishing rate. The agglomerated particle size was controlled by manipulation of the electrical double layer compression. With the addition of salt, particles agglomerated with decreasing electrical repulsive forces. The differences in rheological behavior of ceria slurries were found to be a key parameter in the CMP of a PETEOS film. The removal rate was elevated with a larger size of agglomerated particles. The non-uniformity was increased when using the CeO2 slurry prepared with agglomerated particles.