A silver nanoparticle (AgNP) with good monodispersity was produced by a convenient method for reducing of AgNO 3 with N, N-dimethylacetamide in the presence of polyvinyl pyrrolidone (PVP) as the surface modification agent. The shape and size of the AgNP with reaction time were taken as variables. The surface plasmon band transition was monitored with reaction mixture time at different temperatures. The AgNP crystallinity increases with the reaction time, and the reduction efficiency is very low when AgNP solution is dealt at room temperature even after two days, while it is greatly improved at 160 °C only for 25 min. AgNP modified by the as-synthesized PVP has a face-centered cubic crystalline structure, in which AgNP could develop into a spherical morphology with a very narrow size distribution of 2−11 nm. The preparation provides a new reducing agent to form AgNP with simpler operation and shorter time.