Silver supported on the ZSM-5 (ratio Si/Al = 50) were prepared by impregnation method and characterized by means of numerous analytical techniques: high resolution transmission electron microscopy (HRTEM), Fourier transformed infrared spectroscopy (FTIR) and diffuse reflectance UV-vis spectroscopy (DRS). Catalytic activities of the materials were evaluated in CO oxidation. It was shown that catalytic performance of xAg/ZSM-5 (x = 1, 3, 5, 7 wt.% Ag) depends strongly on Ag loading, among which 7% Ag/ZSM-5 displayed the best properties for the studied reactions. The studies revealed a strong influence of the redox pretreatment temperature on the catalytic activity of the samples. The experiments showed that Ag/ZSM-5 catalyst has a good reproducibility and stability in CO oxidation. Comparison of results of catalytic, structural and spectroscopic measurements allows suggesting Ag+ ions inside zeolite or on the external support surface as well as charged clusters Ag-n(delta+) to be active states of silver in the studied process. The obtained results were compared with previous data for formation of active gold clusters Au-n(delta+) in zeolites. It is important for synthesis of catalytically stable bimetal Au-Ag systems.