Silver nanoparticles (AgNPs) are synthesized in a plasma electrochemical system with an aqueous solution of AgNO3 as anode. 5-Bromouracil, ethanol and dimethyl sulfoxide are added to the solutions for tuning the plasma-induced liquid chemistry. The characteristic localized surface plasmon resonance of the AgNPs is used to investigate the AgNPs formation process. The results indicate that there exists Ag+ reduction and Ag oxidation simultaneously during the AgNPs formation, and the hydrated electrons formed by the dissolution of plasma electrons are the main reducing agents for the Ag+ reduction, while the hydrogen peroxide produced by the plasma-liquid interactions plays a role in etching the formed AgNPs to Ag+. (C) 2018 The Electrochemical society.