Hematoporphyrin monomethyl ether (HMME) is a new photosensitzer with higher photosensitizing ability stronger photodynamic effects and selective uptake into tumor tissue. We analysed photodynamic damages of DNA with HMME as photosensitzer by Raman spectroscopy and obtained at following conclusions: The conformation of DNA has changed from normal B form to modified B′ form. A part of hydrogen-bonds between two bases of pair were broken. The base stacking collapsed to some extent and bases were damaged. Guanine and cytosine were more sensitive to HMME.