A copper(Ⅱ) L-tryptophan complex was synthesized in aqueous solution and characterized by element analysis,differential scanning calorimetry and thermogravimetry,powder X-ray diffraction and Fourier transform infrared spectroscopy.The results showed that the compound had a good stability.A copper ion could combine with two L-tryptophan molecules through the nitrogen of the amine group and one oxyen of the carboxyl group.The low-frequency vibrational spectrum was measured by terahertz time-domain spectroscopy(THz-TDS) at room temperature.Density functional theory was employed to calculate the low-frequency vibrational properties.The result indicated that THz absorption spectrum mainly reflected the collective vibrational modes of the whole molecules including the distortional vibration of indole ring and the side chain.The studies are helpful to understand the interaction of copper ion with amino acid and the role of the copper ion in complex organisms.