A novel route has been found for the formation of silver nanoparticles under hydrothermal conditions from the system of sodium citrate and silver nitrate via trisilver citrate, which is sparingly soluble in water. It was confirmed that the morphology of particulate and crystalline trisilver citrate formed by mixing aqueous solutions of sodium citrate and silver nitrate changed with holding time in water due to Ostwald ripening, and that silver nanorods rather than nanoparticles tended to form from ripened trisilver citrate.