Hydrophobic silica were obtained when, in their synthesis, APS and HMDS were added as modifiers. Besides, their addition caused a large effect on the textural characteristics. The titration of the acidic sites of the modified silicas showed a sharp decrease in acidity compared to the unmodified silica. The TEM micrographs of the synthesized samples showed that the increase in HMDS amount aided to maintain the spherical shape of pure silica, increasing the formation of agglomerations and the primary particle size.