PURPOSE: To facilitate the control of the pore diameter, etc., of a porous silica by forming a porous silica to have a prescribed specific surface area.

CONSTITUTION: An organic compound having ≥2 terminal halogenated acetyl groups and expressed by formula (R is bivalent hydrocarbon group such as 1-8C alkylene, 6-12C arylene and 7-13C aralkylene which may have side chain) is made to react with a silicic acid obtained by the acid treatment of sodium metasilicate, etc., in an organic solvent such as tetrahydrofuran at 10-50°C for 10min to 20hr. The obtained polymer is recovered by filtration and baked at ≥400°C for 1-10 hr in oxygen gas stream, etc., to obtain the objective porous silica having a specific surface area of ≥300m2/g.