The interactions of an anticancer drug,camptothecin with lysozyme and catalase were investigated by the combination of several spectroscopic techniques,including UV-Vis absorption,IR and fluorescence spectra.The results showed that camptothecin could form groundstate complexes with these two proteins and induce the quenching of the intrinsic fluorescence of proteins.The binding constants and the numbers of binding site of camptothecin interacting with lysozyme and catalase at different temperatures were calculated.Their main binding forces were electrostatic interaction and hydrophobic interaction.The distances between camptothecin and tryptophan residues in lysozyme and catalase were determined.Camptothecin showed a higher binding affinity on catalase than it had on lysozyme,as it interacted not only with tryptophan residue,but also with tyrosine residue and heme in catalase.The results also showed that the presence of camptothecin could induce the conformational variation of proteins with a decrease in α-helix secondary structure.