The mode of interaction of emodin and DNA was studied through fluorescence analysis,UV-visible absorption spectra,viscosity measurement and competition experiments with ethidium bromide.When the optimal conditions were set as follows: pH 7.4,ionic strength of 30 mmol/L NaCl,temperature of 37 ℃ and reaction time of 35 min,the fluorescence intensity of emodin was decreased with the increase of DNA concentration.The isosbestic points（380 nm and 475 nm） of emodin was red shifted by 5 nm in the presence of DNA,indicating that the complex of emodin and ctDNA was formed.Meanwhile,the fluorescence spectra of adenine and DNA showed the similar fluorescence quenching to that of DNA,indicating that emodin was embedded in base pairs and the hydrogen bond between adenine and cytosine was damaged.