The　low　bioavailability　of　photosensitizers　(PSs)　and　the　hypoxia　nature　of　tumors　often　limit　the　efficacy　of　current　photodynamic　therapy　(PDT).　Therefore,　improving　the　utilization　of　three　essential　components　(PS,　light,　and　O-2)　in　tumors　will　enhance　PDT　efficacy　substantially.　Herein,　we　have　developed　a　red　blood　cell　(RBC)　biomimetic　theranostic　nanovesicle　(named　SPN-Hb@RBCM)　with　improved　photostability,　accumulation　of　PSs,　and　oxygen　self-supply　ability　to　enhance　PDT　efficacy　upon　near-infrared　(NIR)　laser　irradiation.　Such　a　biomimetic　nanovesicle　was　prepared　by　a　red　blood　cell　membrane　(RBCM)-camouflaged　hemoglobin　(Hb)-linked　semiconducting　polymer　nanoparticle　(SPN-Hb).　The　RBCM　coating　enables　the　long-term　circulation　of　SPN-Hb　due　to　the　membrane-mediated　immune　evasion,　allowing　for　more　effective　PS　accumulation　in　tumors.　Under　808　nm　laser　irradiation,　the　photostable　SPN　can　serve　as　both　a　photodynamic　and　a　second-near-infrared-window　(NIR-II)　fluorescence　imaging　agent;　meanwhile,　the　conjugated　Hb　can　be　used　as　an　oxygen　carrier　to　relieve　tumor　hypoxia　for　enhancing　PDT　efficacy.　In　addition,　Hb　can　also　react　with　the　tumor　microenvironment　overproduced　H2O2　to　generate　cytotoxic　hydroxyl　radicals　((center　dot)OHs)　for　chemodynamic　therapy　(CDT),　which　further　achieve　synergistic　effects　for　PDT.　Thus,　this　study　proposed　a　promising　biomimetic　theranostic　nanoagent　for　enhancing　tumor　oxygenation　and　NIR-II　fluorescence-guided　synergetic　CDT/PDT　against　hypoxic　tumors.