The interaction of hesperidin (HES) or icariin (ICA) and lysozyme (LYS) was studied by fluorescence spectroscopy in physiological buffer solution.It was observed that there was a strong fluorescence quenching effect of hesperidin or icariin on lysozyme.The quenching constants of the drugs with lysozyme were measured at different temperatures,and the quenching mechanism was suggested as dynamic quenching for HES-LYS system and both static and dynamic quenching for ICA-LYS system.The thermodynamic parameters of the interaction of hesperidin or icariin and lysozyme were measured according to the Van’s Hoff equation:the enthalpy change (ΔH) and the entropy change (ΔS) of HES-LYS system and ICA-LYS system were calculated to be 20.29 kJ·mol^-1 and 146.28 J·mol^-1 ·K^-1,and -3.47 kJ·mol^-1 and 81.16 J·mol^-1 ·K^-1,respectively,which indicated that the interaction of hesperidin and lysozyme was driven mainly by hydrophobic force,whereas the interaction of icariin and lysozyme was driven mainly by electrostatic force. It was showed that the reaction processes of the two systems occurred spontaneously sincE_gibbs free energy change (ΔG) values were negative.The binding distances of hesperidin and icariin from the lysozyme tryptophan residue were calculated to be 1.34 nm and 1.24 nm,respectively,based on the Frster’s theory of non-radiation energy transfer.The results of synchronous fluorescence spectra showed that the binding of hesperidin or icariin to lysozyme induced conformational changes in lysozyme.