A model peptide,Tyr-Tyr-Tyr-Tyr(YYYY),was synthesized by Fmoc solid-phase methods,purified and separated by reverse phase high performance liquid chromatography(RP-HPLC),and characterized by ESI-MS analysis.The interaction of peptide with calf thymus DNA(ct-DNA) was investigated by UV-Vis absorption spectra,circular dichroism(CD) and fluorescence spectra.The results showed that,with the increase of peptide concentration,there were a hyperchromic effect on UV spectra,a remarkable fluorescence quenching and a red shift of CD.It is possible that Tyr-Tyr-Tyr-Tyr and Tyr might interact with ct-DNA via the groove binding mode.The interaction between Tyr-Tyr-Tyr-Tyr and ct-DNA,compared with that between Tyr and ct-DNA,is more stronger.