In a continuous flow on-line preconcentration system, trace silver was adsorbed onto activated carbon particles packed in micro colum at pH 1, eluted with 0.3 ml of 10 g/L Na2S2O3 solution and determined by flame atomic absorption spectrometry. For surface water samples, 25 ml sufficed precise determination of silver at level of microgram/L. The relative standard deviation of 10 parallel sample determinations was 6.9%. The proposed method was successfully applied to water samples with recoveries ranging from 93.2% to 104.6% and a throughout of 7-8 sampling/h.