Peroxynitrite(ONOO-)is　a　highly　reactive　nitrogen　species　that　plays　pivotal　roles　in　cell　signal　transduction　and　physiological　or　pathological　progresses.However,commonly　used　ONOO-optical　imaging　probes　are　still　hampered　by　high　background/autofluorescence(fluorescence　probe),short　emission　wavelength,or　poor　selectivity　in　the　case　of　chemiluminescence.Herein,we　report　a　facile　method　to　prepare　an　activatable　chemiluminescence　probe(PPA-PEG)with　good　biocompatibility　and　functionality　for　in　vivo　autofluorescence-free　imaging　of　ONOO-.The　PPA-PEG　consists　of　pyropheophorbide-a(PPA),a　typical　deep　red　photosensitizer　that　acts　as　both　the　recognition　and　signaling　element,and　4-arm　poly(ethylene　glycol)(4-arm　PEG),which　improves　the　biosafety　and　water　solubility　of　probe.These　components　can　self-assemble　into　nanoparticles(namely　PPA-PEG　nanoprobe)in　aqueous　solution.The　PPA-PEG　nanoprobe　showed　an　ultra-low　chemiluminescence　signal　before　interacting　with　ONOO-,but　exhibited　good　selectivity,high　sensitivity　and　a　fast　response　toward　ONOO-.The　PPA-PEG　was　successfully　applied　to　image　cellular　ONOO-changes,as　well　as　the　endogenous　ONOO-changes　in　inflammation　models　and　subcutaneous　or　orthotopic　hepatocellular　carcinoma(HCC)tumors　models　in　living　mice.In　vitro　and　in　vivo　studies　verified　the　good　detection　and　imaging　capabilities　of　PPA-PEG　for　peroxynitrite,demonstrating　suitable　tissue　penetration　and　a　high　signal-to-background　ratio(SBR).Thus,our　nanoprobe　can　serve　as　a　valuable　activatable　chemilu-minescence　imaging　tool　for　studying　important　peroxynitrite-related　chemical　and　biological　applications.