Absorption, fluorescence spectral and viscometric studies have been carried out on the interaction of Morin (2′,3,4′,5,7-pentahydroxyflavone, Scheme 1) and its Cu complex, CuL 2·2H 2O [L=Morin (2′-OH group deprotonated), Scheme 2] with calf thymus DNA. CuL 2 shows different spectral characteristics from that of Morin in the presence of DNA. Increasing fluorescence is seen for CuL 2 with DNA addition whereas decreased fluorescence is observed for Morin. Quenching fluorescence is observed for the DNA–EB system when CuL 2 is added whereas slightly quenched fluorescence is seen for the DNA–EB system with Morin addition. The relative viscosity of DNA and the DNA–EB system increases with the addition of CuL 2. Hypochromism and a smaller shift are observed in the UV–visible spectra of CuL 2 in the presence of DNA and the denatured temperature of DNA is decreased in the presence of CuL 2. The above results suggested that Morin and CuL 2 can both bind to DNA, but the binding mode is different. The complex binds to DNA mainly by intercalation, while Morin binds in a nonintercalating mode.