Abstract: Silver nanoparticles were prepared under the protection of either L-cysteine (L-cyst.) or thioglycollic acid (TGA). The structures of these 2 different states of silver nanoparticles were characterized by UV-VIS spectrophotometry and transmission electron microscope (TEM). As shown by the UV-VIS absorption spectra, absorption maxima at 384 nm and 392 nm were found for the L-cyct.-protected and TGA-protected silver nanoparticles respectively. It was shown by the results of TEM study, the sizes of the L-cyst.-protected and TGA-protected Ag-nanoparticles were found in the ranges of 10-40 nm and 20-30 nm respectively. It was found that significant interaction was observed between the L-cyst.-protected Ag-nanoparticles and eosin Y, giving a bathochromic shift of absorption maximum from 384 nm to 395 nm; and that no interaction between the TGA-protected Ag-nanoparticles and eosin Y was observed. Electrostatic action between the positively charged L-cyst. molecules at the surface of Ag-nanoparticles and the negatively charged eosin Y molecules was proposed as the chemism of the interaction.