Compared　with　the　traditional　treatment,　photodynamic　therapy　(PDT)　in　the　treatment　of　malignant　tumors　has　the　advantages　of　less　damage　to　normal　tissues,　quick　therapeutic　effect,　and　ability　to　repeat　treatments　to　the　same　site.　However,　most　of　the　traditional　photosensitizers　(PSs)　have　severe　skin　photosensitization,　poor　tumor　targeting,　and　low　therapeutic　effect　in　hypoxic　tumor　environment,　which　limit　the　application　of　PDT.　Nanoparticle-based　drug　delivery　systems　can　improve　the　targeting　of　PSs　and　release　drugs　with　controllable　photoactivity　at　predetermined　locations,　so　as　to　achieve　desired　therapeutic　effects　with　minimal　side-effects.　The　present　review　summarizes　the　current　nanoparticle　platforms　for　PDT,　and　offers　the　description　of　different　strategies　including　tumor-targeted　delivery,　controlled-release　of　PSs　and　the　triggered　photoactivity　to　achieve　controllable　PDT　by　nanoparticle-based　drug　delivery　systems.　The　challenges　and　prospects　for　further　development　of　intelligent　PSs　for　PDT　are　also　discussed.　©　2020　Elsevier　B.V.