The interaction mechanisms and structure-activity relationships of lysozyme(LYSO) with psoralen,isopsoralen,5-methoxypsoralen and 8-methoxypsoralen were investigated by ultraviolet spectroscopy,fluorescence spectroscopy,synchronous fluorescence spectroscopy and circular dichroism spectroscopy under the simulative human physiological conditions.The results of ultraviolet difference spectra initially revealed that four furanocoumarin drugs could interact with LYSO.Fluorescence spectra showed that the intrinsic fluorescence of LYSO was significantly quenched by four furanocoumarin drugs and the mechanism of fluorescence quenching was static quenching with non-radiation energy transfer.The 1∶1 complexes were formed between each of the four furanocoumarin drugs and lysozyme.The binding parameters of four furanocoumarin drugs(psoralen,isopsoralen,5-methoxypsoralen and 8-methoxypsoralen) with LYSO at 310 K were as follows:the binding constants(K) were 1.02×104,6.95×104,7.05×104 L?mol-1 and 8.60×104 L?mol-1,and the binding distance(r) were 4.36,4.75,5.25 and 5.89 nm,respectively.The major driving forces were hydrogen bond and Van der Waals.The different positions of furan ring and methoxy led to the different interactions of four furanocoumarins drugs and lysozyme,and the order of the interaction strengths between each of four furanocoumarin drugs and lysozyme were as follows:8-methoxypsoralen＞5-methoxypsoralen＞isopsoralen＞psoralen.The results of circular dichroism indicated that four furanocoumarin drugs had impacts on the secondary structure of LYSO.Psoralen,isopsoralen,5-methoxypsoralen and 8-methoxypsoralen made the content of α-helical structure of LYSO reduce by 27.1%,11.5%,10.6% and 0.917%,respectively.The results of synchronous fluorescence spectra demonstrated that psoralen,5-methoxypsoralen and 8-methoxypsoralen could combine with LYSO and had effects on the conformation of LYSO,while isopsoralen had a less effect on the conformation of LYSO than the other three furanocoumarin drugs.