Excessive　production　of　reactive　oxygen　species　such　as　H2O2　is　the　pathological　basis　of　chronic　inflammatory　diseases,　as　well　as　bacterial　infection-induced　inflammation.　Therefore,　the　in　situ　H2O2　level　is　a　reliable　biomarker　of　inflammatory　responses,　and　its　real-time　measurement　can　monitor　disease　progression　and　improve　therapeutic　outcomes　in　inflammation-linked diseases.　However,　the　currently　used　strategies　for　the　diagnosis　of　inflammation　is　mainly　through　routine　blood　test,　which　are　limited　in　determining　the　inflammation　status　and　cannot　provide　comprehensive　quantitative　information.　In　this　work,　a　novel　H2O2-responsive　theranostic　nanoplatform　comprising　Ag　shell　coated　Pd-tipped　gold　nanorods　(Au–Pd@Ag　NR)　is　developed.　The　etching　and　oxidation　of　the　Ag　shell　by　H2O2　release　the　Ag　ions,　which　effectively　kill　bacteria　in　vivo　and　trigger　their　absorption　variation　at　700　and　1260 nm.　The　ratiometric　photoacoustic　(PA)　imaging　at　1260　and　700 nm　(PA1260/PA700)　accurately　quantifies　H2O2　in　a　mice　model　of　bacterial　infection　and　abdomen　inflammation,　even　in　a　rabbit　model　of　osteoarthritis.　The　H2O2　activated　second　near-infrared　(NIR-II)　PA　images　of　the　probe　can　further　precisely　differentiate　the　inflammation　region　and　normal　tissue.　This　nanoplatform　not　only　can　quantify　H2O2　during　inflammation　but　also　act　as　a　potent　antibacterial　agent.　©　2020　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim