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High stability and dispersibility colloidal silver nanoparticles in pure inorganic system were prepared by wet chemical reduction of AgNO3 with NaBH4 and with sodium hexametapnosphate as dispersant through optimizing the sodium hexametapnosphate concentrations and the molar ratios of NaBH4 and AgNO3. Feature absorptions of the colloids obtained from UV-vis analysis appears at below 400 nm. TEM shows that colloidal silver nanoparticles have narrow particle size distribution, and a mean particle size below 10 nm with single spherical-like shape. The colloidal silver nanoparticles prepared in traditional organic systems are easily adsorbed by surface active agents or ionic polymers which could not be easily removed and thus the residues would directly influence the physical and chemical properties of the colloidal silver nanoparticles. The dispersant of sodium hexametapnosphate adsorbed on the colloidal silver nanoparticles prepared in pure inorganic system is a water loving reagent which could be removed easily for preparing pure colloidal silver nanoparticles. This method is simple and effective for preparing colloidal silver nanoparticles without any control of pH, temperature, ultrasound, etc