Thermodynamic studies have been made on the effect of Cr(+3) on the conformation and structure of bovine beta lactoglobulin-A, (Blg-A) in 50 mM sodium chloride solution at 27 degrees C using isothermal titration calorimetry (ITC), circular dichroism (CD) and fluorescence spectroscopy. There is a set of six identical and independent binding sites for Cr(+3) by a dissociation binding constant of 124 microM and the molar enthalpy of binding -17.8 kJ/mol. Circular dichroism studies do not show any significant change in the secondary structure of the protein after the binding of chromium ion on the Blg-A. Fluorescence spectroscopy studies do not show any considerable change in the tertiary structure of Blg-A due to the increasing of Cr(+3) in low concentration. However, occupation of fourth and fifth binding sites for chromium ions induce partially unfolding in the tertiary structure of the protein resulted from solvent - exposed hydrophobic patches on BLG-A.