Interaction of ioliquiritigenin（ISL）, which is the main active component of a commonly used traditional Chinese medicine（TCM） Glycyrrhiza uralensis Fisch. with bovine serum albumin（BSA） has been investigated. The quenching mechanism of fluorescence of bovine serum albumin by ISL was discussed. The binding sites number n and apparent binding constant K were measured by fluorescence quenching method. The thermodynamic parameters ΔH^0, ΔG^0, ΔS^0 at different temperatures were calculated. The distance r between donor（bovine serum albumin） and acceptor（ISL） was obtained according to F？rster theory of non-radiation energy transfer. The results of synchronous fluorescence spectra and UV-vis absorption spectra show that the conformation of bovine serum albumin has been changed.
