Nanomaterials with enzyme-like activity (nanozymes) are known to be suitable alternatives for natural enzymes tolerating unfavorable pH and temperature conditions. The enzyme-like activity of CeO₂ nanoparticles was already reported and used in electrochemical sensing, where the peroxidase or oxidase-like activities of CeO₂ NPs are mainly used. This work aims to justify the role/s that CeO₂ may play in electrochemical sensing as a nanozyme and acts as a mediator. To this end, a reduced graphene oxide-CeO₂ was prepared and used in two electrochemical sensing configurations. In first configuration, H₂O₂ reduction was catalyzed at the glassy carbon electrode modified with the rGO-CeO₂ nanocomposite (rGO-CeO₂ NC). The reduction current obtained upon the presence of H₂O₂ was attributed to a mediator role having a linear range of 100.0–800.0 µmol L⁻¹ with a limit of detection (LOD) and limit of quantification (LOQ) of 15.9 µmol L⁻¹ and 52.9 µmol L⁻¹, respectively. In another configuration, glucose oxidase was used as a model enzyme with the rGO-CeO₂ NC. The oxidation signal obtained upon adding glucose was attributed to the electron-accepting role of the CeO₂ NPs. The analytical figures of merit obtained for both configurations indicated their high sensitivity, selectivity, and reproducibility. The linear detection range for the nanozyme-enzyme cascade system was 100.0–800.0 µmol L⁻¹ with a LOD and LOQ of 18.7 µmol L⁻¹ and 62.3 µmol L⁻¹, respectively. Moreover, the flow injection analysis was enabled due to the short response time in analysis with the prepared sensor. The possibility for applying the developed nanozyme in nanozyme-enzyme cascade system in clinical and food analysis for determination of glucose was verified by studying the interference of various compounds similar to glucose in structure and typical drugs taken by diabetic patients.