In this work, we report a novel naked-eye and fluorescent dual-readout glucose sensing platform based on the bifunctional peroxidase mimicking and ON–OFF fluorescence of Pd nanoparticle-decorated graphitic C₃N₄ nanosheets (PdNPs/g-C₃N₄). The PdNPs/g-C₃N₄ hybrid not only exhibited a strong peroxidase-like activity to catalyze colorless o-phenylenediamine (OPD) into its yellow product OPDox in the presence of H₂O₂, but it also acted as a turn-off fluorescent sensor for the assembly of the generated OPDox on g-C₃N₄. When coupled with glucose oxidase (GOx), the platform could provide both visual and fluorescent responses for glucose specifically. Under optimal conditions, the platform was able to detect the target at concentrations as low as 50 μM and 0.4 μM in the linear ranges of 50–2000 μM and 1–1000 μM with the naked eye and a fluorometer, respectively. The developed platform integrates the equipment-free merit of naked-eye observation with the excellent performance of fluorometric analysis well, providing a new and powerful tool for both rough assessment and accurate detection of glucose in diabetes management and other applications.