To obtain a hydrous silicic acid capable of improving tensile strength and abrasion resistance of rubber, a rubber composition having improved tensile strength and abrasion resistance and a pneumatic tire using the rubber composition having improved tensile strength and abrasion resistance.

This silicic acid has 120-220 specific surface area (m2/g) by a BET method, 4.0-5.5 value C in the relation V=(1.5/100)×BET+C between Sears titration amount V (NaOH titration amount ml/g) and a specific surface area BET (m2/g) by a BET method and the ratio A/B of a peak value A (angstrom) of pore diameter measured by an N2 method to a peak value B (angstrom) of pore diameter measured by a mercury method of ≥1.4. This rubber composition is obtained by formulating 100 pts.wt. of a natural rubber and/or a diene-based synthetic rubber with 5-100 pts.wt. of the hydrous silicic acid. This pneumatic tire is obtained by using the rubber composition as a tread rubber.