Self-assembled　phototheranostic　nanomaterials　used　for　photodynamic　therapy　(PDT)　have　attracted　increasing　attention　owing　to　their　several　advantages.　Herein,　we　developed　a　novel　strategy　for　size-tunable　self-assembled　nanophotosensitizers　for　PDT　through　a　simple　method.　A　series　of　switchable　self-assembled　nanophotosensitizers　(NanoPc90,　NanoPc40,　NanoPc20,　and　NanoPc10)　of　different　particle　sizes　were　readily　prepared　based　on　an　amphiphilic　silicon(IV)　phthalocyanine　(SiPc)-biotin　conjugate　by　regulating　the　amount　of　the　Cremophor　EL　surfactant　used.　The　photoactivities,　including　fluorescence　and　reactive　oxygen　species　(ROS),　of　the　self-assemblies　could　be　regulated　by　the　particle　size.　The　self-assemblies　could　be　specifically　disassembled　by　tumor-overexpressing　biotin　receptors,　leading　to　the　recovery　of　quenched　photoactivities.　Demonstrated　by　the　competitive　assay,　the　self-assemblies　were　able　to　enter　HepG2　cells　through　a　biotin-receptor-mediated　pathway,　followed　by　biotin-receptor-triggered　fluorescence　recovery　at　the　cellular　level.　Moreover,　the　particle　size　could　also　affect　the　in　vitro　and　in　vivo　PDT　effects　and　tumor　targeting.　The　photocytotoxicity　of　NanoPc20　against　HepG2　cells　was　more　potent　compared　to　that　of　NanoPc90　because　of　its　strong　intracellular　fluorescence,　higher　intracellular　ROS　generation,　and　different　subcellular　localization.　In　addition,　NanoPc20　showed　higher　in　vivo　tumor　targeting　and　photodynamic　therapeutic　efficacy　than　NanoPc90.　This　work　would　provide　a　valuable　reference　for　the　development　of　self-assembled　nanophotosensitizers　for　cancer　diagnosis　and　therapy.　©　2019　American　Chemical　Society.