The effect of Cd ions on salmon sperm DNA was studied by means of circular dichroism(CD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy. The CD spectral and fluorescent probe-acriflavine results indicate that the DNA underwent a conformation change upon the addition of Cd ions. XPS and Raman studies reveal that there existed interactions between Cd ions and the phosphate groups of the DNA. In addition, a new band appeared at 803 cm-1in the Raman spectra, which can be attributed to characterizing "marker" band of A-DNA. It is concluded that Cd ions can be coordinated by the phosphate groups of the DNA and induce the conformation changes of the DNA from B-DNA to A-DNA.