60,Co γ rays irradiation method was used to prepare nano-particle silver in aqueous solution. The structure, morphology, size and the melting point had been characterized by X-ray diffractometer (XRD), Transmission Electron Microscopy (TEM), and Differential Scanning Calorimeter (DSC). The results show that the size of gained particles decreases with increment of PCM concentration and the melting point becomes smaller with decrement of the particle size, while the concentration is changed from 0.6 g/100 mL to 2.2 g/100 mL. The smallest size of silver nano-particle is 19.9 nm, and the melting point is 126.18°C when the concentration is 2.2 g/100 mL. The pure silver nano-particles have been obtained at different pH. It is found that the pH of the aqueous solution has no effect on the constitution of the sample.