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A high-concentration silver colloidal nanoparticles with a narrow size distribution were obtained using [Ag(NH3)2]+-PVP(poly (N-vinyl-2-pyrrolidone)) solution via the synergistic action of UV and heat excitation. The nucleation and growth of the silver nanoparticles were monitored by UV-vis. absorption spectroscopy. The results show surface plasma resonance peaks of silver nanoparticles are located at about 419 nm. Transmission electron microscopy (TEM) reveals that most of the particles possess spherical shape with an average size of about 1.32 nm and standard deviation 0.53 nm. Moreover, the pH value of the obtained samples is nearly neutral, which will lead to a more extensive application.