A relation between the current oscillation of iron and the Fe (II) and Fe (III) dissolutions during the active-passive transition in sulfuric acid solution (pH1) was investigated by channel flow double electrode (CFDE). Firstly, potentiodynamic polarization curves of iron in the solutions containing various concentrations of chloride ions were measured in order to find experimental conditions where the current oscillation appeared. Secondly, the time-series of the current oscillation in the active-passive transition potential region were measured, and Fe (II) and Fe (III) dissolved from the iron electrode were detected simultaneously. It was found that not only the working electrode current but also the dissolution rates of Fe (II) and Fe (III) oscillated. In the solutions without chloride ion and containing low concentration of chloride ion, Fe (III) dissolves previous to the current oscillation, contrary to this, the dissolution of Fe (II) shows a delay from the current oscillation. On the other hand, in the solution containing chloride ions more than 0.02mol/dm3, passivation was not observed on the polarization curve. In the high chloride concentration, the dissolution rates of both Fe (II) and Fe (III) show the delay from the current oscillation. On the basis of the above mentioned results, the current oscillation mechanism of the iron and the influence of chloride ion on the current oscillation were discussed.