Graphitic　carbon　nitride　(g-C3N4)　has　been　shown　as　a　promising　visible-light　photosensitizer　for　photodynamic　therapy　(PDT)　application.　Nevertheless,　its　therapeutic　efficiency　is　limited　by　the　low　efficiency　of　visible-light　utilization.　To　overcome　this　issue,　3-amino-1,2,4-triazole-derived　graphitic　carbon　nitride　nanosheets　(g-C3N5　NSs)　are　prepared　for　PDT　application.　The　addition　of　nitrogen-rich　triazole　group　into　the　g-C3N4　motif　significantly　makes　the　light　absorption　of　g-C3N5　NSs　red-shift　with　the　band　gap　down　to　1.95　eV,　corresponding　to　a　absorption　edge　at　a　wavelength　of　636　nm.　g-C3N5　NSs　generate　superoxide　anion　radicals　(O2•–)　and　singlet　oxygen　(1O2)　under　the　irradiation　of　a　low-intensity　white　light　emitting　diode.　Owing　to　the　high　efficiency　of　visible-light　utilization,　g-C3N5　NSs　show　about　9.5　fold　photocatalytic　activity　of　g-C3N4　NSs.　In　vitro　anticancer　studies　based　on　the　results　of　CCK-8　assay,　Calcein-AM/PI　cell-survival　assay　and　photo-induced　intracellular　ROS　level　analysis　in　living　HeLa　cells　demonstrate　the　potential　of　g-C3N5　NSs　as　a　low-toxic　and　biocompatible　high-efficient　photosensitizer　for　PDT.　©　2020　Elsevier　B.V.