In this paper,the SERS(Surface enhanced Raman scattering) method is for the first time employed as a probe to investigate the interaction between the photosensitizer ALPCS and the nucleic acid bases.The advantage of this method is that it can Provide important information on the sensitive slids and damaging process which can't be achieved by other methods.The obtained results suggest that G(Guanine) is most senSitive and vulnerable and the A(Adenine) is less vulnerable,while C(Cytedne) and U(Uracil) are totally not sensitive to the photosensitizer at all. The experiments have confirmed that singlet oxygen, the product of ALPCS photodynamic reaction, pays an importmant role in the damaging process of G and A.