Atomically dispersed nanozymes have garnered immense attention within the biomedical field, while precisely designing these nanozymes and elucidating their intricate structure-performance relationships of their structures and antibacterial performance remain the formidable challenges. Herein, we fabricated defect-rich graphene supported layered Ir cluster nanozymes for antibacterial applications. Steady-state kinetic experiments revealed that the layered Ir clusters exhibited the higher catalytic efficiency of 1.16 mM⁻¹·s⁻¹ with 3,3',5,5'-tetramethylbenzidine (TMB) and 0.18 mM⁻¹·s⁻¹ with H₂O₂, compared to Ir nanoparticle (0.55 and 0.1 mM⁻¹·s⁻¹) and the atomically dispersed Ir single-atom nanozyme (SAzyme) (0.3 and 0.039 mM⁻¹·s⁻¹) and other previously reported single-atom nanozymes. Moreover, both experimental results and density functional theory studies disclosed that the layered Ir clusters exhibited the enhanced ability to facilitate the conversion of hydrogen peroxide into hydroxyl free radicals, signifying the higher catalytic efficiency than that on Ir nanoparticles and Ir single-atoms. Notably, the Ir cluster nanozyme with robust peroxidase-like activity had 100% antimicrobial rate against E. coli and S. aureus, underscoring its potential applications in antibacterial fields.