Chemisorption of propionic acid vapors by an iron impregnated MCM-41 porous silica leads to the formation of iron-propionate species that upon pyrolysis can be transformed into gamma -Fe2O3 nanoparticles of uniform size (similar to 150 Angstrom) and homogeneously dispersed on the external surfaces of the porous silica support. The effect of the carboxylic acid nature on the size of the magnetic particles was examined. The magnetically modified MCM-41 solid retains its crystallinity and large surface area and can be functionalized with various organosilicon ligands, e.g., (CH3O)(3)SiCH2CH2CH2NHCH2CH2NH2, to produce novel reconstructed MCM-41 derivatives without destroying the magnetic properties of the parent material. The various steps in the synthesis and functionalization, as well as the nature, size, and location of the particles into the final solids were studied by means of IR and XRD, bulk magnetic measurements, Mossbauer, BET, and TEM techniques.