An aluminosilicate with the MCM-41 structure (AlMCM-41) was used as a host for the synthesis of cobalt sulfide nanoparticles. Cobalt sulfide nanoparticles were introduced in host by ion exchange and hydrothermal methods. Products (CoSAlMCM-41) were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), EDX, IR, BET and UV-vis spectroscopy. The results show that CoS nanoparticles encapsulated into channels of AlMCM-41 material by hydrothermal synthesis and they grow outside the mesopore AlMCM-41 matrix by ion-exchange methods. Absorption peaks at higher energy than the fundamental absorption edge of bulk CoS indicate quantum confinement effect in nanoparticles as a consequence of their small size. The absorption spectra show that the optical band gap for CoS nanoparticles by hydrothermal and ion-exchange methods are 3.73 and 4.89, respectively. (C) 2008 Elsevier B.V. All rights reserved.