PURPOSE: To produce a hydrophobic wet type synthetic silicic acid by simply and economically treating a surface of a wet type synthetic silicic acid with silicone oil without requiring heating or by heating at a relatively lower temp. and also without adding a catalyst such as alkali.

CONSTITUTION: In a production method of the hydrophobic wet type synthetic silicic acid treating the surface of the wet type synthetic acid with the silicone oil, the wet type synthetic silicic acid incorporating ≥0.5 pts.wt. Al expressed in terms of Al2O3 for 100 pts.wt. SiO2, is used. The wet type synthetic silicic acid incorporating ≥0.5 pts.wt. Al expressed in terms of Al2O3 for 100 pts.wt. SiO2 and the silicone oil are mixed and subsequently are left, as it is, at the normal temp. or 100°C.