A kinetic spectrophotometric method for the determination of trace phenanthroline was proposed. The method is based on the inhibition of phenanthroline to the discoloring reaction of EBT oxidized by hydrogen peroxide in the dilute acetic acid solution. At the same time, the kinetic parameters were studied in detail. Under optimum experimental conditions, the linear range is 0.003-0.08 mg x L(-1), and the detection limit is 4.0 microg x L(-1). The method is simple, rapid, and easy to operate. The method was applied to the determination of trace phenanthroline in water samples with satisfactory results.