The interactions of lysozyme with ephedrine，pseudoephedrine and methylephedrine，as well as their structure-activity relationship were investigated by fluorescence spectrometry under simulative physiological conditions.The binding constant，the number of binding sites and the thermodynamic parameters were calculated and the effects of ephedrine，pseudoephedrine and methylephedrine on the conformation of lysozyme were studied.The results showed that the endogenous fluorescence of lysozyme was significantly quenched by ephedrine，pseudoephedrine and methylephedrine.The mechanism of fluorescence quenching was static quenching.The 1∶1 complex was formed between each amphetamine and lysozyme.The binding constants K of ephedrine，pseudoephedrine and methylephedrine were 511×103，404×103,280×103 L?mol-1，respectively.According to the theory of Fster dipole-dipole non radiation energy transfer mechanism，the binding distances r were 0241,0350,0422 nm，respectively.The enthalpy change（ΔH）were-123,-126,-521 kJ?mol-1，the entropy change（ΔS） were-329，-339,-103 J?mol-1?K-1，respectively.The results demonstrated that the configuration and substituted methyl in amphetamines played an important role in the interaction between amphetamines with lysozyme，and the order of the interaction strength between the amphetamines and lysozyme was as follows：ephedrine＞pseudoephedrine＞methylephedrine.The hydrogen bond and Vander Waals force were the major driving force between amphetamines and lysozyme.The influences of three amphetamines on the conformation of lysozyme were also investigated with synchronous fluorescence spectra.The result showed that the conformation of lysozyme was not changed by three amphetamines.