To obtain precipitated silicic acid with a homogeneous hydrophobicity by mixing an aq. suspension of precipitated silicic acid with an aq. silane emulsion and drying the mixture and by imparting a loss of drying, a loss on ignition, a methanol wettability, and a carbon content, each in a specified range, to the resultant silicic acid.

An aq. suspension of precipitated silicic acid is mixed with an aq. silane emulsion, and the mixture is dried, if necessary batchwise with a spray drier or a spin flash drier, to give a hydrophobic precipitated silicic acid having a loss of drying of 2.0-10 wt.%, a loss on ignition of 2-25 wt.%, a methanol wettability of 20-80 wt.%, and a carbon content of 1-30 wt.%. The aq. silane emulsion contains 1-80 wt.% alkoxysilane of the formula (e.g. triethoxyoctylsilane), 1-20 wt.% anionic or nonionic surfactant, 0.1-5 wt.% buffer (e.g. sodium carbonate), 1-95 wt.% water, etc. In the formula, R1 is a 1-3C alkyl: R3 is an 8-16C alkyl or phenyl; and a is 0-3.