Magnetic single-domain γ-Fe 2 O 3 nanoclusters have been prepared by (i) coprecipitation of ferrous and ferric salts encapsulated within sol-gel derived silica (SiO 2 ), and (ii) oxidation of ferrous cations incorporated in a sulfonated, ion-exchange porous silica matrix. In the first method, a SiO 2 coating was formed on the Fe 2 O 3 nanoclusters by hydrolysis and condensation of tetraethoxysilane. In the second route, sulfite (SO − 3 ) functionalized silica was synthesized from a modified sol-gel precursor resulting in a porous gel with a narrow pore size distribution. The SiO 2 coating and sulfonated SiO 2 matrix provide the means for homogeneous dispersion of Fe 2 O 3 clusters. The SiO 2 -coated Fe 2 O 3 nanoclusters are spherical with 4–5 nm diameters. Acicular crystalline Fe 2 O 3 nanoclusters with diameters of ∼4 nm and lengths of 10–20 nm were found in the porous sulfonated gel matrix. Magnetization and Mössbauer studies indicated that the γ-Fe 2 O 3 /SiO 2 nanocomposites are superparamagnetic. The magnetic properties can be manipulated via the matrix structure and synthesis conditions.