<p>Real-time and accurate detection of drug-induced liver injury is critical for early intervention and treatment, yet clinically applicable visualization methods remain scarce. Based on the difference in glutathione (GSH) content between the normal liver and the livers with different-grade injury, we report a GSH-activated <i>T</i>₁-weighted magnetic resonance imaging (MRI) nanoprobe (C-MnO), which can be used for non-invasive real-time in vivo magnetic resonance imaging (MRI) of the consumption of GSH in the liver, thereby being applied for the graded diagnosis of liver injury. Due to the presence of abundant disulfide bonds in C-MnO, the <i>T</i>₁ MRI signal around it remained “quenched” until encountering GSH. When C-MnO enters the body and is efficiently absorbed by the liver, it will disassemble and degrade under the action of GSH, thereby activating the <i>T</i>₁ MRI signal. Therefore, this nanoprobe provides an effective visual method for capturing the changes in GSH content during different degrees of liver damages at an early stage, which is beneficial for the graded diagnosis and precision treatment of drug-induced liver injury. Comprehensive in vitro and in vivo studies demonstrate that C-MnO, as a GSH-activated <i>T</i>₁ MRI nanoprobe, enables real-time monitoring and graded diagnosis of drug-induced liver injury, effectively addressing current clinical limitations in the detection of liver injury.</p> Graphical Abstract <p></p>