MCM-41 molecular sieve materials have been investigated by means of impedance spectroscopy. Dielectric response of water confined in MCM-41 molecular sieve materials showed a power law dispersion, which was assigned to ac conductivity. This process, which occurs at temperatures close to room temperature, was found in all our investigated samples with the pore diameters ranging from 2.0 to 3.7 nm. Obtained values of the imaginary part of the complex dielectric permittivity were much larger than that of the bulk water. Such a phenomenon can be explained by the electrical response characteristic of the microstructural electrical network formed by water and hosting mesoporous silica material. The real part of conductivity has been calculated, and the influence of the pores size to electric conductivity and its mechanisms are discussed. (c) 2006 Elsevier Ltd. All rights reserved.