A stable nanosilver solution was prepared, using PEG10000 as stabilizer and NaBH(4) as reducer. In pH 6.6 Na(2)HPO(4)-NaH(2)PO(4) buffer solution containing PEG10000 and NaCl, the nanosilvers (AgNPs) were aggregated to form the stable nanosilver-aggregation (AgNPA) that could conjugate with 4-mercaptopyridine (MPy) to obtain an AgNPA-MPy surface-enhanced Raman scattering (SERS) probe with a strong SERS peak at 1097 cm(-1). When Hg(2+) concentration increased, the SERS intensity at 1097 cm(-1) decreased linearly as the stable complex of [Hg(MPy)(2)](2+) was formed and the AgNPA particles precipitate to the bottom. The decreased SERS intensity was linear to Hg(2+) concentration in the range of 50-3000 nmol/L. Based on this, a new sensitive SERS method has been proposed for the determination of trace Hg(2+) in the water sample, with satisfactory results.