To provide an aqueous, waterproofing agent which can give the good waterproofness to a porous material even exposed to heavy winds and rains or contacted with snow for a very long period.

The aqueous, waterproofing agent is an emulsion of an organosilicon compound containing (A) an alkylalkoxysilane, (B) an aminoalkyl group-containing alkylalkoxysilane and (C) a surfactant. A weight ratio of components (A) to (B), both of the organosilicon compound, is 1:0.2-0.4 and that an mount of the surfactant (C) is 1-20 wt.% relative to the total sum of components (A) and (B) of the organosilicon compound.