Photodynamic　therapy　(PDT)　is　recognized　as　a　powerful　method　to　inactivate　cells.　However,　the　photosensitizer　(PS),　a　key　component　of　PDT,　has　suffered　from　undesired　photobleaching.　Photobleaching　reduces　reactive　oxygen　species　(ROS)　yields,　leading　to　the　compromise　of　and　even　the　loss　of　the　photodynamic　effect　of　the　PS.　Therefore,　much　effort　has　been　devoted　to　minimizing　photobleaching　in　order　to　ensure　that　there　is　no　loss　of　photodynamic　efficacy.　Here,　we　report　that　a　type　of　PS　aggregate　showed　neither　photobleaching　nor　photodynamic　action.　Upon　direct　contact　with　bacteria,　the　PS　aggregate　was　found　to　fall　apart　into　PS　monomers　and　thus　possessed　photodynamic　inactivation　against　bacteria.　Interestingly,　the　disassembly　of　the　bound　PS　aggregate　in　the　presence　of　bacteria　was　intensified　by　illumination,　generating　more　PS　monomers　and　leading　to　an　enhanced　antibacterial　photodynamic　effect.　This　demonstrated　that　on　a　bacterial　surface,　the　PS　aggregate　photo-inactivated　bacteria　via　PS　monomer　during　irradiation,　where　the　photodynamic　efficiency　was　retained　without　photobleaching.　Further　mechanistic　studies　showed　that　PS　monomers　disrupted　bacterial　membranes　and　affected　the　expression　of　genes　related　to　cell　wall　synthesis,　bacterial　membrane　integrity,　and　oxidative　stress.　The　results　obtained　here　are　applicable　to　other　types　of　PSs　in　PDT.