Bioimaging　guided　photothermal　therapy　possesses　great　promise　for　lesion　diagnosis　and　effective　treatment.　However,　distinguishing　lesion　from　normal　tissues　for　precise　cancer　therapy　remains　a　great　challenge.　Herein,　a　stimulation-responsive　assembled　Ag2S　vesicle　(Ag2S　Ve)　is　proposed　by　self-assembly　of　Ag2S　quantum　dots　(QDs)　coated　with　pH-sensitive　copolymer　thiolated　polystyrene-co-poly(4-vinylpyridine).　The　Ag2S　Ve　shows　significant　absorption　enhancement　in　the　near-infrared　(NIR)　region　and　strong　fluorescence　inhibition　in　the　second　near　infrared　(NIR-II)　region.　Triggered　by　the　acidic　environment,　the　release　of　Ag2S　QDs　promptly　mediates　the　quenched　NIR-II　fluorescence　from　＇off＇　to　＇on.＇　In　vivo　studies　reveal　that　the　theranostic　Ag2S　Ve　can　be　specifically　activated　in　acidic　tumor　tissues,　whereas　it　exhibits　nonfunctional　in　normal　tissues.　Larger　sizes　endow　vesicles　a　higher　tumor　accumulation　efficiency　and　controllable　disassembly　shows　illuminating　characteristics　toward　lesion　tissues,　which　provides　an　innovative　therapeutic　strategy　for　activated　NIR-II　fluorescence　imaging　guided　cancer　therapy.　©　2021　Wiley-VCH　GmbH