The interaction between the small biomolecules of berberine hydrochloride (BH) and bovine hemoglobin (BHb) were studied by fluorescence spectrum and UV–Vis absorbance spectroscopy under the human physiological conditions.It was observed from Figure 1 that a progressive decrease in the fluorescence intensity was caused by quenching with the addition of BH.The insert in Figure 1 shows that within the investigated concentrations range,the results agree with the Stern–Volmer equation,which indicated that the fluorescence quenching of BHb by BH is a result of the formation of BH–BHb complex.The thermodynamic parameters ΔH,ΔG,ΔS at different temperatures were calculated (Table 1),and van der Waals and hydrogen bonds play an important role to stabilize the complex.