Magnetic rattle-type particles, comprising magnetite or metallic iron in nonporous dense hollow silica microspheres, were fabricated by using sol-gel reactions of alkylsilyl trichlorides around droplets of aqueous iron nitrate solution in a water-in-oil emulsion. After evaporation of water within the silica capsules to leave iron salts, calcination of the dried sample was conducted to transform into a hematite (alpha-Fe2O3) core and porous hollow silica shell by losing alkyl groups of polyalkylsiloxane. Hydrogen gas penetrated through the silica shell and reduced hematite to magnetite (Fe3O4) at 310 degrees C and metallic iron (alpha-Fe) at 450 and 500 degrees C. The reduction at 310 degrees C resulted in largest magnetization at 12 kOe among the present magnetic particles. The core magnetic compounds were enclosed by a dense silica shell, which was transformed from porous silica by annealing in nitrogen at 700 degrees C. Because the magnetic particles were encapsulated by the dense silica shell, the magnetism was shown even after immersion in 1 M HCI for a longer period. Acidity was successfully imparted on this magnetic capsule by anchoring sulfonic groups covalently for its use as magnetically collectable solid acid.