The influence of adding KCI on the silver sols was studied by transmission electron microscopy (TEM). It was found that the Ag atoms on the surfaces of the colloidal silver particles were transported to other positions of the silver surfaces after adding KCI, and the sur-feccs of colloidal silver particles were covered with an atomic group layer which had some kind of structure. At the same time, a chain-like colloidal aggregation in Ag sols was induced by KCI. This was compared with the case of adding pyridine. Also we discussed the effect of adding KCI on the SERS signals of molecules adsorbed on colloidal silver particles.