Abstract: Monodispersed silver nanoparticles were obtained by a simple route in water with PVP as the capping agents, hydrazine hydrate as the reducing agents, silver nitrate solution as the silver source. The characteriztion of as-synthesized silver nanoparticles were studied by the transmission electron microscopy, UV-vis spectuam, X-ray powder diffraction and laser particle size analyzer. The results indicated that the obtained silver nanoparticles were small with the narrowly distribution. The concentration of silver nitrate, the consumption of PVP and hydrazine hydrate played the important roles in the size and morphology of silver nanoparticles. Smallest silver naopartilces were obtained when the consumption of PVP and hydrazine hydrate was 0.2 g and 0.1 g,respectively, and the concentration of silver nitrate was 150 mg/L.