Photodynamic　therapy(PDT)　is　a　cancer　therapeutic　modality　that　utilizes　photosensitizers(PSs)　and　molecular　oxygen　upon　irradiation　with　light　to　generate　cytotoxic　reactive　oxygen　species　leading　to　damage　of　the　target　tissues　and　cells.　Activatable　photosensitizers(aPSs)that　are　inactivated　initially,　can　only　be　activated　by　tumor-associated　stimuli,　such　as　tumor-associated　specific　enzymes,　acidic　pH,　nucleic　acid,　to　achieve　targeting　diagnosis　and　treatment.　The　aPSs　have　become　a　hot　spot　in　the　field　of　medical　photosensitizers　because　of　its　higher　selectivity.　In　this　paper,　we　will　summarize　the　recent　development　of　aPSs,　and　analyze　their　structure-activity　relationships,　expecting　to　provide　a　reference　for　the　future　studies.　©　2018,　Editorial　Office　of　Progress　in　Chemistry.　All　right　reserved.