Abstract: In the medium of 0.04 mol/L sulphuric acid and 0.01 mol/L benzoglycolic acid, silver(Ⅰ) was reduced photochemically to silver sol and benznglycolic acid was oxidized photo chemically to benzaldehrde. Thesilver sol exhibits strongly a resonance scattering peak at 525 nm. The intensity is proportional to silver concentration in the range of 0.1 and 4.0 μg/mL. This method has been applied to the detemination of silver in wastewater. The photochmical reaction has been investigated by resonance scattering spectroscopy, UV spectropho-tometry and oscillopolarography. The reaction mechanism and the phenomenon of scattering were discussed.