Smart　phototheranostic　nanomaterials　are　of　significant　interest　for　high-quality　imaging　and　targeted　therapy　in　the　precision　medicine　field.　Herein,　a　nanoscale　photosensitizer　(NanoPcM)　is　constructed　through　the　self-assembly　of　morpholine-substituted　silicon　phthalocyanine　(PcM)　and　albumin.　NanoPcM　displays　a　turn-on　fluorescence　depending　on　the　acid-induced　abolition　of　the　photoinduced　electron　transfer　effect　(change　in　molecular　structure)　and　disassembly　of　the　nanostructure　(change　in　supramolecular　structure),　which　enables　low-background　and　tumor-targeted　fluorescence　imaging.　In　addition,　its　efficient　type　I　photoreaction　endows　NanoPcM　with　a　superior　immunogenic　photodynamic　therapy　(PDT)　effect　against　solid　tumors.　The　combination　of　NanoPcM-based　PDT　and　αPD-1-based　immunotherapy　can　efficiently　inhibit　tumor　growth,　reduce　spontaneous　lung　metastasis,　and　trigger　abscopal　effects.　This　study　should　provide　a　perspective　for　the　future　design　of　nanomaterials　as　promising　phototheranostics　for　cancer　imaging　and　therapy.　©　2022　American　Chemical　Society