Acute liver failure (ALF) is characterized by rapid hepatic dysfunction, primarily caused by drug-induced hepatotoxicity. Due to the lack of satisfactory treatment options, ALF remains a fatal clinical disease, representing a grand challenge in global health. For the drug repositioning to ALF of mesalamine, which is clinically approved for the treatment of inflammatory bowel disease (IBD), we propose a supramolecular prodrug nanoassembly (SPNs). Mesalamine is modified with a functional peptide of the FRRG sequence. The resulting mesalamine prodrugs form nanoassemblies solely through intermolecular interactions, ensuring high drug loading capacity and reducing the potential toxicity associated with the carrier materials of conventional nanoparticle systems. In acetaminophen (APAP)-induced ALF mouse models, the SPNs predominantly accumulate in injured target tissues owing to the nanoparticles' propensity to target the liver. Subsequently, cathepsin B overexpressed in hepatocytes by drug-induced inflammation triggers the release of mesalamine from the nanoassemblies enzymatic cleavage, resulting in remarkable therapeutic efficacy. Meanwhile, nonspecific drug release in healthy cells is inhibited due to their relatively lower cathepsin B expression, which helps prevent the exacerbation of the ALF by minimizing adverse events related to drug exposure. This study provides valuable insights into designing rational nanomedicine for repurposing mesalamine in ALF treatment, potentially inspiring further research to discover effective and safe therapeutic options for patients.