The kinetics of the Fe(III)/Fe(II) redox reaction were studied in solutions with different total sulfate concentration in all forms (pSO’(4)) and pH values. The variation found in the values of the kinetic parameters and diffusion coefficient is explained through the influence of the different Fe(III)-sulfate complexes predominant in the solution : Fe(SO4)(2)(-), FeSO4+ and FeHSO42+.