Ag triangular nanoplates were synthesized by photoirradiation to AgNO3 ethanol solution in the presence of polyvinylpyrrolidone (PVP) under anaerobic conditions at room temperature. High-resolution SEM and TEM observations revealed that thin Ag equilateral triangular nanoplates, each of which was a single crystal with sharp corners and flat faces presented by {1 1 1} planes, were produced. Analyses of XAFS and XPS have shown that these nanoplates are protected by coordination of O atoms in PVP molecules, not being oxidized as Ag2O. The nanoplates are inherently stable, though they were easily truncated and dissolved if mixed with oxygen or water. (C) 2009 Published by Elsevier B. V.