Silver (Ag) nanodecahedrons have been synthesized for the first time by liquid-phase reduction of AgNO3 with assistance of polyvinylpyrrolidone (PVP) in a large scale. The edge size of Ag decahedrons is estimated to be ca. 80 nm. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) have been employed to elucidate the five-twinned structure of Ag decahedrons. The results show that the Ag decahedrons capped by PVP molecules hold five-twinning structure with distinct twinning boundaries. The growth process of Ag decahedrons has been investigated and their growth mechanism has been proposed. Combined with our previous reports on Ag nanowires with pentagonal cross section, it is revealed that the Ag nanodecahedrons might be assembled from five tetrahedrons step by step. Further studies on the role of PVP conformation in different solution reduction systems are required. (c) 2006 Elsevier B.V. All rights reserved.