Objective: To study the mechanism of interaction between phloretin and human serum albumin (HSA). Method: The binding constant

binding site and binding distance was investigated by fluorescence spectrometry. Result: Phloretin could induce an endogenous fluorescence quenching of HSA under a mechanism of static quenching. The binding constants were determined to be 1.518 1×105(298 K)

9.441 2×104(303 K) and 5.417 8×104(313 K)L·mol-1

respectively. The binding site (n) was about 1.The thermodynamic parameters suggested that the interaction forces between phloretin and HSA were mainly hydrophobic force. According to förster nonradiation energy transfer mechanism

the binding distance was estimated to be 4.27 nm. The results obtained from synchronous fluorescence spectra showed that phloretin had only a slight influence on the HSA conformation. The common ions could affect the binding constant of phloretin-HSA complex. Conclusion: Fluorometric analysis is a good method for the study on phloretin-HSA binding reaction. It has the advantages of high speed and high sensitivity.