Abstract: Anew indicator reaction catalyzed by silver has been studied. When silver is present K₄Fe(CN)₈reacts with o-phenanthroline in the solution of dilute H₂SO₄, the mechanism may be represented as follow:Fe(CN)₆^4-+3(o-Phen)^AgFe(o-Phen)₂(ornge)+6CN^-and trace silver could be estimated with the reaction.The apparent activation energies of catalytic and uncatalytic reaction are 64.15 and 96.89 kJ·mol^-1, respectively, was calculated by Arrhenius Formula.Compared with other methods, this one is higher sensilivity and selectivity. The sensitivity is 8×10^-12g·ml^-1.The method has been used for the determination of silver in geological samples with satisfactory results .The average standard deviation of determination is 0.024 and the average coefficient variation 2.43%.