An aluminosilicate with the MCM-41 structure (A1MCM-41) was used as a host for the synthesis of nickel metal nanoparticles. Initially, ion exchange in aqueous solutions allows the introduction of nickel cations into A1MCM-41, and then reduction with sodium borohydride produces nanometer-sized nickel metal particles. Products (Ni-A1MCM-41) were characterized by elemental analysis, transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and magnetic susceptibility. Ni-A1MCM-41 was found to have a Ni:Al:Si ratio of ca. 1:4:28. The nickel metal particles were 1-2 nm in diameter and showed superparamagnetic behavior with a blocking temperature (T-b) of 5 K.