A simple and environmentally friendly method was developed for preparing colloidal silver nanoparticels in aqueous solutions using silver nitrate, sodium alginate and glucose as silver precursor, capping agents and reducing agents respectively. The formation of silver nanoparticles was observed by change of color from colorless to yellow. The silver nanoparticles were characterized by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and X-ray diffraction (XRD). The TEM images showed that, the particles are small, well dispersed and spherical in shape with a narrow distribution from 3 nm to 12 nm. The XRD demonstrated that the obtained metallic nanoparticles are single crystalline silver nanoparticles. The effects of the reaction time, reaction temperature and the concentration of silver ion and reducing agent on the particle size were investigated by the UV-vis spectra. The present process is an excellent candidate for the preparation of silver nanoparticles because it is simple, pollutant free, inexpensive and easy to perform. The method may be extended to other noble metals, such as Au, Pd and Pt, for medicinal, industrial and technological applications.