PURPOSE: To obtain a composite polymer suitable for a liquid chromatography supporter by polymerizing sodium silicate, a specific monofunctional monomer and a difunctional monomer in an aqueous medium in the presence of an organic liquid, a thickener, a polymerization agent in an aqueous solution.

CONSTITUTION: Sodium silicate, at least one monofunctional vinyl, acryl or aryl monomer (e.g. acryl amide) and a difunctional acryl or aryl crosslinked monomer arc simultaneously or successively polymerized in an aqueous solution in the presence of a non-mixable organic liquid (e.g. soybean oil) and/or a thickener (e.g. glycerol) as necessary, thereby producing the objective composite polymer containing 20 to 80 wt.% of silica, 80 to 20 wt.% of a three dimensional crosslinked acryl and/or aryl copolymer.