ABSTRACT ZnO nanoparticles (NPs) were synthesized via a green biochemical method using Corymbia citriodora leaf extract as a reducing and stabilizing agent. The biosynthesized ZnO NPs were characterized by SEM and XRD. An electrochemical H2O2 biosensor was fabricated by modification of a glassy carbon electrode using our proposed ZnO NPs. The electrochemical sensor showed excellent detection performance towards trace amounts of H2O2, demonstrating that it could potentially be used in clinical applications.