The interaction of Fe3+ with bovine serum albumin (BSA) in physiological buffer (pH=7.4, Tris-HCl) was studied by fluorescence and UV-vis absorption spectroscopy at 298, 306 and 313 K. The quenching mechanism of bovine serum albumin by Fe3+ was found to be a static quenching process. The binding constant K and number of binding sites n were measured by fluorescence quenching method. The thermodynamic parameters such as entropy change (ΔS), enthalpy change (ΔH) and Gibbs free-energy change (ΔG) for the reaction were also obtained. The electrostatic force played a major role for Fe3+-BSA, and the Gibbs free-energy change (ΔG) were always negative indicated that the binding was spontaneous process（r=5.10 nm）. From the synchronous fluorescence spectra, it can be found that the binding of Fe3+ with BSA induced the conformational changes in BSA.

bovine serum albumin; fluorescence quenching; thermodynamic parameters; the synchronous fluorescence spectra