The data of Mössbauer spectroscopic measurements in rapidly frozen 57FeIII nitrate solutions containing indole-3-acetic acid (IAA) are presented. The results obtained provide direct evidence that iron(III) is gradually reduced by IAA with the formation of soluble iron(II) complex. It has been found that further drying of the solution in air results in complete re-oxidation of iron(II) with the formation of iron(III) complex. The structure of the complexes obtained and their possible role in solubilization and transformation of iron species in soil in the presence of IAA secreted by soil microorganisms into the environment are also discussed.