Ag2O particles with different polyhedral shapes including octahedron, truncated octahedron, and cube were successfully synthesized by a simple wet-chemical method using silver nitrate, ammonia, and sodium hydroxide as raw materials at room temperature. Simply by tuning the concentration of starting materials, the shape of Ag2O particles evolved from octahedron to cube, and the size gradually decreased from 1-2 mu m to 400-700 nm. As examples for promising applications, the antibacterial activities of the as prepared Ag2O polyhedral particles were preliminarily studied. It has been found the antibacterial activity of Ag2O particles against E. coli depends on the shape of Ag2O particles, demonstrating that the surface structure or Ag2O particles affects the antibacterial activity.