Multifunctional　nanoplatforms　with　integrated　diagnostic　and　therapeutic　functions　have　attracted　tremendous　attention.　Especially,　the　second　near-infrared　(NIR-II)　light　response-based　nanoplatforms　hold　great　potential　in　cancer　theranostic　applications,　which　is　because　the　NIR-II　window　provides　larger　tissue　penetration　depth　and　higher　maximum　permissible　exposure　(MPE)　than　that　of　the　well-studied　first　near-infrared　(NIR-I)　window.　Herein,　we　for　the　first　time　present　a　two-dimensional　(2D)-nanoplatform　based　on　Cu2MnS2　nanoplates　(NPs)　for　magnetic　resonance　imaging　(MRI)/multispectral　optoacoustic　tomography　(MSOT)　dual-modal　imaging-guided　photothermal　therapy　(PTT)　of　cancer　in　the　NIR-II　window.　Methods:　Cu2MnS2　NPs　were　synthesized　through　a　facile　and　environmentally　friendly　process.　A　series　of　experiments,　including　the　characterization　of　Cu2MnS2　NPs,　the　long-term　toxicity　of　Cu2MnS2　NPs　in　BALB/c　nude　mice,　the　applications　of　Cu2MnS2　NPs　for　in　vitro　and　in　vivo　MRI/MSOT　dual-modal　imaging　and　NIR-II　PTT　of　cancer　were　carried　out.　Results:　The　as-synthesized　Cu2MnS2　NPs　exhibit　low　cytotoxicity,　excellent　biocompatibility　as　well　as　high　photothermal　conversion　efficiency　(similar　to　49.38%)　and　outstanding　photostability.　Together　with　their　good　T-1-shortening　effect　and　strong　absorbance　in　the　NIR-I　and　NIR-II　region,　the　Cu2MnS2　NPs　display　high-contrast　imaging　performance　both　in　MRI　and　MSOT　(900　nm　laser　source).　Moreover,　the　subsequent　in　vitro　and　in　vivo　results　demonstrate　that　the　Cu2MnS2　NPs　possess　excellent　PTT　efficacy　under　1064　nm　laser　irradiation　with　a　low　power　density　(0.6　W　cm(-2)).　In　addition,　the　detailed　long-term　toxicity　studies　further　confirming　the　safety　of　Cu2MnS2　NPs　in　vivo.　Conclusion:　We　have　developed　a　new　2D　Cu2MnS2　NPs　as　multifunctional　theranostic　agents　for　MRI/MSOT　dual-modal　imaging-guided　PTT　of　cancer　in　the　NIR-II　window.　Such　biocompatible　Cu2MnS2　NPs　might　provide　a　new　perspective　for　exploring　new　2D-based　nanoplatforms　with　improved　properties　for　clinical　applications　in　the　future.