Reactive oxygen species (ROS) play a crucial role in lipid peroxidation and the initiation of ferroptosis, markedly affecting chemotherapeutic drug resistance. However, the mechanisms by which ROS function and are sensed remain poorly understood. In this study, we identified O-GlcNAc transferase (OGT), a key enzyme in protein O-GlcNAcylation, as a sensor for ROS during ferroptosis. The ROS-induced oxidation of OGT at C845 in its catalytic domain activates the enzyme. Once activated, OGT O-GlcNAcylates FOXK2, enhancing its interaction with importin α, which facilitates FOXK2's nuclear translocation and binding to the SLC7A11 promoter region. This, in turn, boosts SLC7A11 transcription, thereby inhibiting ferroptosis. The elevated OGT-FOXK2-SLC7A11 axis contributes to tumorigenesis and resistance to chemoradiotherapy in hepatocellular carcinoma (HCC). Our findings elucidate a ROS-induced oxidation-O-GlcNAcylation cascade that integrates ROS signalling, O-GlcNAcylation, FOXK2-mediated SLC7A11 transcription and resistance to both ferroptosis and chemoradiotherapy.