The incidence and prevalence of inflammatory bowel disease (IBD) increases steadily worldwide. There is an urgent need for effective and safe IBD therapies. Accelerated resolution of inflammation is a new strategy for the management of inflammatory diseases. For effective and safe IBD treatment, herein a smart nanotherapy (i.e. oxidationâresponsive nanoparticles containing a proresolving annexin A1âmimetic peptide Ac2â26, defined as AON) is developed, which can release packaged Ac2â26, in response to highly expressed reactive oxygen species (ROS) at diseased sites. AON effectively protects Ac2â26 from degradation in the enzymeârich environment of the gastrointestinal tract. By delivering this nanotherapy to the inflamed colons of mice with IBD, siteâspecific release and accumulation of Ac2â26 in response to high levels of ROS at the inflammatory sites are achieved. Mechanistically, the Ac2â26âcontaining, oxidationâlabile nanotherapy AON effectively decreases the expression of proinflammatory mediators, attenuates trafficking and infiltration of inflammatory cells, promotes efferocytosis of apoptotic neutrophils, and increases phenotypic switching of macrophages. Therapeutically, AON reduces symptoms of inflammation, accelerates intestinal mucosal wound healing, reshapes the gut microbiota composition, and increases shortâchain fatty acid production. Additionally, oral delivery of this nanomedicine shows excellent safety profile in a mouse model, conferring the confidence for further development of a targeted precision therapy for IBD and other inflammatory diseases.