Abstract: Kaempferol-copper (Ⅱ) complex (kaempferol-Cu) was synthesized with kaempferol and CuCl₂·2H₂O, and its chemical properties were characterized by UV spectroscopy, infrared spectroscopy,¹H-NMR and differential thermal analysis. The free radical activity of the complex was evaluated by DPPH method.The result showed that the UV-visible, Infra-red absorption spectra of the complex both produced a significant bathochromic shift. The ¹H NMR data shows the 3-OH groups was not presented in the complex,and the proton signals of the complex shifted to lower frequencies relative to that of the free kaempferol.The differential thermal-thermal analysis confirming that the stoichiometric ratio for the complexation of Cu (Ⅱ) and kaempferol was 1:1, and the complex contains three coordinated water molecules. In the range of experimental concentration(1.0~3.5 mol/L), the IC₅₀ of DPPH free radical of the kaempferol and complex was 1.63×10^-4, 1.51×10^-4 mol/L respectively. The synthesized complex was coordinated with a Cu (Ⅱ) ion via the 3-OH and 4-oxo groups, kaempferol-Cu exhibited more potent antioxidant effect than kaempferol.