A simple one-step reduction method was explored to synthesize silver particles of different size. During synthesis, Polyvinylpyrrolidone (PVP) and CH 2 O were used as the protective agent and the reducing agent, respectively. It is found that the reaction parameters including the concentration of PVP and AgNO 3 , the amount of ammonia and the reaction temperature has great influence on the size and uniformity of silver particles. By careful tuning the reaction parameters, mono-disperse silver particles with the size of 40–2000nm can be obtained controllably. It is considered that there were two growth modes: diffusional growth and aggregation.