The charging and admix behaviors of a series of surface-modified R972 silicas (modified by two positive charge control agents (CCAs) and nine negative CCAs prepared by the fluidized bed spray process (1:10 wt. ratio of CCA to R972) were studied with unpigmented styrene–butadiene toner (∼9 μm). Concurrent to xerographic measurements, the morphologies of the modified silica samples and the resulting toners were examined by TEM and SEM microscopy, respectively. Results showed that when the CCA was homogeneously distributed in the silica sample, it dominated the charging and admix properties of the resulting toner. Because the actual CCA concentration was only 0.05wt%., the observation clearly demonstrated that the approach of using CCA-modified silicas is one of the most effective ways to impart charging in toner. When the CCA was not distributed homogeneously in the silica sample, the toner resin dominated the charging and admix properties. The inefficacy of the CCA in this case is attributable to a surface area effect. The importance of the physical state or the distribution of the CCA in the silica sample was further illustrated in the case of KTPB (potassium tetraphenylborate)-modified silicas. Although the silica sample prepared by the fluidized bed spray process was inhomogeneous, we were able to homogenize the distribution of KTPB in R972 using a solution-coating technique. The solution-coated KTBP/R972 sample not only showed great enhancement in negative tribo (e.g., from ∼27 to ∼95 μC/g), it also reduced the admix time from 15 to 2 min