Carbon-based　dot　nanoclusters　(CDCs)　are　reported　for　the　first　time.　The　morphologies　of　the　obtained　CDCs　are　characterized　using　transmission　electron　microscopy　and　atomic　force　microscopy.　It　is　found　that　the　CDCs　are　composed　of　dozens　of　carbon-based　dots　(CDs),　which　are　connected　together　through　the　sp(3)-hybridized　carbon　atoms.　When　compared　with　free　CDs,　the　obtained　CDCs　have　higher　defect　densities.　As　a　result,　the　UV-vis　absorption　edge　of　the　CDCs　is　extended　to　around　700　nm,　and　the　maximum　fluorescence　wavelength　red-shifts　to　570　nm.　Furthermore,　the　CDCs　show　a　high　singlet　oxygen　(O-1(2))-generation　capability　(quantum　yield　of　about　0.13)　under　visible　light　irradiation.　The　long-wavelength　emission　and　the　excellent　photostability　give　the　obtained　CDCs　great　application　potential　in　cell　imaging,　and　the　wide　UV-vis　absorption　band　and　high(1)O(2)-generation　capability　allow　the　obtained　CDCs　to　work　as　effective　photosensitizers　in　photodynamic　cancer　therapy.