Photodynamic　therapy　(PDT)　is　a　new　therapeutic　approach　for　cancer　treatment.　Its　mechanism　relies　on　three　elements:　photosensitizer,　light　and　oxygen.　Under　aerobic　conditions,　a　suitable　wavelength　of　light　activates　the　photosensitizer　that　results　in　the　formation　of　reactive　oxygen　species　(ROS).　We　herein　report　that　PDT　with　a　zinc　phthalocyanine　(ZnPc)　photosensitizer　coupled　with　2,4,6-tris　(N,　N-dimethylaminomethyl)　phenoxy　(TAP),　termed　as　ZnPc(TAP)(4),　has　the　ability　to　photodegrade　DNA　in　tumor　cells　via　hydroxyl　radicals　produced　under　the　red　light　irradiation,　resulting　in　effective　elimination　of　tumor　cells.　Furthermore,　the　high-efficient　anti-tumor　effect　of　ZnPc(TAP)(4)　was　verified　in　a　human　breast　adenocarcinoma　cell　line　MCF-7　tumor-bearing　animal　model.　To　the　best　of　our　knowledge,　this　is　the　first　time　that　destructive　effects　of　hydroxyl　radicals　produced　by　PDT　on　DNA　of　tumor　cells　has　been　documented,　which　may　open　up　new　avenues　of　antitumor　therapy　on　eliminating　the　DNA　of　tumor　cells.