Background:　Surgery　is　considered　to　be　a　potentially　curative　approach　for　gastric　cancer.　However,　most　cases　are　diagnosed　at　a　very　advanced　stage　for　the　lack　of　typical　symptoms　in　the　initial　stage,　which　makes　it　difficult　to　completely　surgical　resect　of　tumors.　Early　diagnosis　and　precise　personalized　intervention　are　urgent　issues　to　be　solved　for　improving　the　prognosis　of　gastric　cancer.　Herein,　we　developed　an　RGD-modified　ROS-responsive　multifunctional　nanosystem　for　near-infrared　(NIR)　imaging　and　photothermal　therapy　(PTT)　against　gastric　cancer.　Methods:　Firstly,　the　amphiphilic　polymer　was　synthesized　by　bromination　reaction　and　nucleophilic　substitution　reaction　of　carboxymethyl　chitosan　(CMCh)　and　4-hydroxymethyl-pinacol　phenylborate　(BAPE).　Then,　it　was　used　to　encapsulate　indocyanine　green　(ICG)　and　modified　with　RGD　to　form　a　smart　multifunctional　nanoparticle　targeted　to　gastric　cancer　(CMCh-BAPE-RGD@ICG).　The　characteristics　were　determined,　and　the　targeting　capacity　and　biosafety　were　evaluated　both　in　vitro　and　in　vivo.　Furthermore,　CMCh-BAPE-RGD@ICG　mediated　photothermal　therapy　(PTT)　effect　was　studied　using　gastric　cancer　cells　(SGC7901)　and　SGC7901　tumor　model.　Results:　The　nanoparticle　exhibited　suitable　size　(approximate　to　120　nm),　improved　aqueous　stability,　ROS-responsive　drug　release,　excellent　photothermal　conversion　efficiency,　enhanced　cellular　uptake,　and　targeting　capacity　to　tumors.　Remarkably,　in　vivo　studies　suggested　that　CMCh-BAPE-RGD@ICG　could　accurately　illustrate　the　location　and　margin　of　the　SGC7901　tumor　through　NIR　imaging　in　comparison　with　non-targeted　nanoparticles.　Moreover,　the　antitumor　activity　of　CMCh-BAPE-RGD@ICG-mediated　PTT　could　effectively　suppress　tumor　growth　by　inducing　necrosis　and　apoptosis　in　cancer　cells.　Additionally,　CMCh-BAPE-RGD@ICG　demonstrated　excellent　biosafety　both　in　vitro　and　in　vivo.　Conclusion:　Overall,　our　study　provides　a　biocompatible　theranostic　nanoparticle　with　enhanced　tumor-targeting　ability　and　accumulation　to　realize　NIR　image-guided　PTT　in　gastric　cancer.