The interaction between guanidine chloride and bovine serum albumin（BSA） in aqueous solution as well as the denaturation process of BSA were studied with fluorescence spectroscopy at 30 ℃ and two pHs.The fluorescence spectroscopic data were analyzed with the methods described by Pace.The unfolding fraction（fu）,denaturation equilibrium constant（Ku） and free energy of unfolding（ΔGu）of protein were calculated.The transition midpoint（c1/2） ,steepness of the transition region（m） and free energy of unfolding（ΔGH2O） were also obtained.The results indicated that the denaturation of BSA was induced by guanidine chloride through direct and indirect effects,the interaction between guanidine chloride and BSA was divided into three stages.When the guanidine chloride concentrations reached 60 mol?L-1,the unfolded fraction fu was about 1 and the BSA was completely denaturated.