The tribo-charge performance of treated silicas made from a selection of different aqueous colloidal silicas and treated with several different silanes is shown to be principally a function of the logarithm of the water partial pressure during development. However, no correlation between the tribo-charge behavior and the silica surface water concentration was found. Surface treatment with silanes containing certain ionizable functional groups can have a dramatic impact on tribo-charge behavior that differs significantly from treatment with only simple alkane-type silanes. A series of SEM micrographs is also presented, which show that the treated colloidal silicas fully retain their original size and shape and that the silica particles have excellent dispersibility and adhesion to the toner particle.