A simple and sensitive first order kinetic-spectrop hotometric method is proposed for the determination of Iron (II) in nanogram amounts. This method is based on the catalytic effect of Iron (II) on the oxidat ion of o-anisidine by potassium bromate in acidic medium ( HCl). The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of o-anisidine solution at 420 nm by fixed time method (20 minutes). The proposed method allows determination of Iron (II) in the ran ge of 0.501-4.010 μg/ml with good precision and accuracy. The optimization of the operating conditions regarding concentrations of the reagents, temperatu re and interferences are also investigated. The reaction was found to be first order in o-anisidine , Iron (II) and bromate. The rate of the reaction is found to have an inverse dependence on hydrogen ion concentration. The pseudo-first order rate constants are determined at different temperatures and thermodynamic parameters were evaluated . A possible mechanism has been proposed. The method wa s applied to the determination of Iron (II) in Pharmaceutical samples. The results obtained were i n excellent agreement with the standard methods such as atomic absorption spectrometry. The coeffic ient of variance and % error were in the range of 0.998 -0.294 and 0.20-0.25 % respectively. The anal ytical results obtained were satisfactory.