Immunogenic　cell　death　(ICD)　and　tumour-infiltrating　T　lymphocytes　are　severely　weakened　by　elevated　reactive　oxygen　species　(ROS)　in　the　tumour　microenvironment.　It　is　therefore　of　critical　importance　to　modulate　the　level　of　extracellular　ROS　for　the　reversal　of　immunosuppressive　environment.　Here,　we　present　a　tumour　extracellular　matrix　(ECM)　targeting　ROS　nanoscavenger　masked　by　pH　sensitive　covalently　crosslinked　polyethylene　glycol.　The　nanoscavenger　anchors　on　the　ECM　to　sweep　away　the　ROS　from　tumour　microenvironment　to　relieve　the　immunosuppressive　ICD　elicited　by　specific　chemotherapy　and　prolong　the　survival　of　T　cells　for　personalized　cancer　immunotherapy.　In　a　breast　cancer　model,　elimination　of　the　ROS　in　tumour　microenvironment　elicited　antitumour　immunity　and　increased　infiltration　of　T　lymphocytes,　resulting　in　highly　potent　antitumour　effect.　The　study　highlights　a　strategy　to　enhance　the　efficacy　of　cancer　immunotherapy　by　scavenging　extracellular　ROS　using　advanced　nanomaterials.　Reactive　oxygen　species　in　the　tumour　microenvironment　can　have　an　immunosuppressive　effect.　Here,　the　authors　devise　a　nanoparticle　that　anchors　to　the　extracellular　matrix　within　tumours　and　scavenges　reactive　oxygen　species,　resulting　in　an　enhanced　immune　response　within　the　tumour.