Coating of gamma-Fe(2)O(3) nanoparticles with SiO(2) layer by wet chemical synthesis and its applications to protein separation and purification were investigated. The average particle size of gamma-Fe(2)O(3) core was 20 nm and SiO(2) layer thickness was 5 nm. The band of Off radicals on SiO(2) layer was detected between 3600 and 3200 cm(-1) in wave numbers, which showed that the surface property of coated nanoparticles was similar to that of conventional fumed silica. Finally, the feasibility of gamma-Fe(2)O(3)/SiO(2) nanoparticles for magnetic separation media in various bio processes was discussed in terms of structural and functional properties such as pore structure and magnetic properties.