gamma-Fe2O3 nanocrystallites dispersed in an amorphous silica matrix have been successfully prepared for the first time by mechanical activation of a chemistry-derived precursor at room temperature. The initial 10 h of mechanical activation triggered the formation of nanocrystallites of Fe3O4 in a highly activated matrix. Increasing the mechanical-activation time led to a phase transformation from Fe3O4 to gamma-Fe2O3. The gamma-Fe2O3 phase was well established after mechanical activation of the precursor for 30 h. Further increasing the mechanical-activation time to 40 h induced the formation of alpha-Fe2O3. The mechanical-activation-grown gamma-Fe2O3 nanocrystallites were similar to10-12 nm in size and well dispersed in the silica matrix, as observed using TEM. They demonstrated superparamagnetic behavior at room temperature when measured using a Mossbauer spectrometer and a vibrating sample magnetometer (VSM). In addition, the gamma-Fe2O3 derived from 30 h of mechanical activation exhibited a value of saturation magnetization as high as 62.6 emu/g.