Abstract: Mechanism of the interaction of the coordination complex of samarium(Ⅲ) and calcein (CAI in short) with DNA was studied by spectrophotometry,fluorophotometry and viscositometry using acridine orange (AO in short) as probe.As shown by experimental results,the coordination complex formed between Sm(Ⅲ) and CAI has an octahedronal molecular structure with its binding mole ratio (nSm(Ⅲ)∶nCAI) of 1 to 3,and the Sm(Ⅲ)-CAI complex reacts with DNA to form an association complex with the combination constant (K) of 2.09×104L·mol-1.As shown by ploting according to the Scatchard equation,the characteristics of the complex between Sm(Ⅲ)-CAI and DNA belongs to types of intercalation of middle strength and partial electrostatic.