Monodisperse and spherical micro-size silver powder, which has narrow size distribution and high purity, was prepared by using silver nitrate as metal source, L-ascorbic acid as reductant and sodium sulfate as dispersant. The aim of this paper was to study the simultaneous effects of pH (2-6), silver nitrate concentration [AgNO3] (0.25-0.75 mol/L), dropping time t(d) (5-15 min) and their interactions on properties of silver particles. In order to detect factor interactions and optimize these parameters, Box-Behnken design of experiments (a response surface methodology) was used. Synthesized silver powders were characterized by a laser particle size analyzer (LPSA), a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). After surveying the experiment data and regression analysis of the data, a mathematical model was derived for optimizing particle size. The optimum condition was: [AgNO3], 0.75 mol/L; pH, 6; and t(d), 5 min. The predicted particle size was 139 mu m and the experimental particle size was 138 mu m at the optimum condition, which showed that the model agreed well with the experimental data. It is found that the [AgNO3] and dropping time have a positive effect and the pH value has a negative influence on the particle size. The possible mechanism for the formation of novel spherical silver particles is explored. (C) 2014 Elsevier B.V. All rights reserved.