The functionalization of organic ligands on nanoparticles (NPs) to create metal-organic interfaces can tune the activity and selectivity of catalytic reactions. Comparing to well-documented electronic and steric contribution of organic ligands, the coverage of ligands is also a significant factor but has been rarely investigated. Herein, we employ two methods, potential cycling (Figure 1c) and thermal annealing, to judiciously remove the surface ligands from gold nanoparticles (AuNPs) and systematically investigate the influence of surface coverage of ligands on the catalytic performance. Potential cycling enables a mild removal of ligands without changing the size of AuNPs (Figure 1a and Figure 1b) and thus provides ideal models to identify the intrinsic influence of surface coverage of ligands on oxygen reduction reaction (ORR). The ORR activity and selectivity is quantitatively evaluated by plotting half potential and transferred electron number versus the surface coverage of ligand. Thermal annealing at different temperatures produces different sized AuNPs with various surface ligand coverage. However, it is suggested that the surface coverage of ligand plays a more significant role on ORR than the particle size of AuNPs. Capping AuNPs with oleylamine and sodium citrate and the reverse poisoning clean AuNPs with thiol, butylamine and CTAB further reveal the difference of ORR activity/selectivity of the capped AuNPs is directly related to the surface coverage of the ligands regardless the diverse chemical nature of these ligands (Figure 1d). This work highlights that the surface coverage of ligands should be considered to be an important factor accounting for metal-organic interfaces in addition to chemical nature of the ligand itself. Figure 1