To obtain the subject composite particles increased in specific surface area and pore volume by neutralizing a granular material of a magnetic substance and a partially neutralized material of an alkali silicate obtained by allowing a mixed solution of silicic acid alkali aqueous solution with magnetic substance particles, a water-soluble polymer and an acid aqueous solution of stand.

A silicic acid alkali aqueous solution of the formula Na2O.mSiO2.nH2O [(m) is 1-4; (n) is 0 or an arbitrary integer] is mixed with 1-100wt.% (based on SiO2) magnetic substance particles having 0.2-50μm number - average particle diameter (by electron microscope method), 0.1-1.0g/cc apparent density, 1-100 Oe saturated magnetization and 105 to 109Ω.cm volume specific resistance, a water-soluble polymer and an acid aqueous solution to afford a mixed solution having pH10.2-11.2. The mixed solution is allowed to stand at 0-10°C for 1-50hr to deposit a granular material comprising a partially neutralized material of an alkali silicate and a magnetic substance and the granular material is separated and neutralized with an acid to provide the objective magnetic substance-amorphous silica composite particles having 200-800m2/g BET specific surface area, 18-1,000 pore radius and 0.1-0.6ml/g pore volume.