Size-selected silver clusters (Ags) have been produced in two different zeolite matrixes (mordenite and erionite) with circular and elliptic channels (cross sections with axes 0.63 x 0.63 and 0.65 x 0.70 nm, respectively(1)). The clusters were detected by UV-vis diffuse reflectance spectra from characteristic short-wavelength peaks (principally at 290 and 320 nm). These peaks contrast strongly with the plasmon resonances, familiar for nanometer-sized silver particles. Observed dusters are stable over an extremely long period (more than 5 years of storage under ambient conditions for Ag-erionite samples). Recently, the specific geometries of these Ags clusters-were determined by means of EXAFS.(2) MO LCAO (molecular orbital with a linear combination of atomic orbital) calculations for the ground states of a series of Ag-8 clusters with different geometries were performed. The most probable Ag-8 cluster structure fitting the zeolite voids was selected. Such clusters have electronic transition energies consistent with the experimental data, and the cluster geometries are similar to those obtained from the EXAFS measurements.