A glassy carbon electrode covered with thiol-functionalized polysiloxane film modified by electrodeposited lead nanoparticles was used for determination of Ag(I) by square-wave anodic stripping voltammetry. The sol-gel methodology based on co-condensation of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) in the presence of cetyltrimethylammonium bromide (CTAB) was applied to synthesize an organosilica sol that was used to modify electrode surface. Silver ions were accumulated on the electrode surface by complexation with thiol groups and then simultaneously deposited with Pb nanoparticles by reduction at -0.85 V. The Pb nanoparticles used as modifier of polyslioxane film significantly improved the electrochemical performance of the sensor. Under optimized conditions, the voltammetric signal was proportional to the Ag(I) concentration in the range of 0.0093 to 1.85 nmol L-1 with excellent limits of detection and quantification of 1.2 pmol L-1 and 4.1 pmol L-1 after 90 s of accumulation on the electrode surface covered with thiol-functionalized polysiloxane film, respectively. The proposed method was applied for determination of Ag(I) in river water samples collected from Bystrzyca and Vistula without mineralization and a total silver concentration in commercially available silver-containing products.