The catalytic behavior of silver ion for the roaction betwoon porsulfate and cerous ion was utilized for the dotormination of silver by speetrophotometric method.The test solution containing 5 ml of 0.025 M cerous salt, 1-7 ml of 2 N sulfuric acid, various amount of silver ion and 10.00 ml of 0.05M persulfate was diluted to 25.00 ml.Undor the optimum condition, the reaction rate (or slope of D-t line) is proportional to the silver ion concentration in the ranges 4 to 60 μg/ml (for 410 nm) and 0.2 to 24 μg/ml (for 330nm)with the maximum deviation of 11.6%.The effects of temperature and various foreign ions have also been investigated.