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Deposition of platinum monolayers on Au substrate (denoted as Au@PtML) has been shown an efficient catalyst design strategy for the electrocatalysis of alcohol oxidation due to presumed 100% utilization of Pt atoms and substrate-enhanced catalytic activities. However, the atomic structure and stability of Pt (sub)monolayers on realistic nanoparticulate Au surface still remains elusive. Here, we reveal coverage-dependent atomic structures and electrocatalytic stabilities of Pt submonolayers (sML) on Au nanoparticles for methanol oxidation reaction (MOR) by using high-resolution transmission electron microscopy combined with energy dispersive X-ray spectrum imaging and electrochemical techniques. At lower Pt coverages, the PtsML more resembled monatomic-thick layers, whereas higher Pt coverages above 0.5 ML resulted in 3D subnanometer Pt nanoclusters leading to lower Pt utilization efficiencies. Moreover, the Au@PtsML catalysts with Pt coverage below 0.5 ML showed higher structural and electrocatalytic stability during MOR electrocatalysis. As a result, increasing the Pt coverage beyond 0.5 ML brought in no obvious gain in the overall catalytic performance. Our results suggest that the Au@Pt0.5 ML catalyst appears to be a more reasonable MOR catalyst than previously reported Au@Pt1.0 ML catalyst, providing more rational catalyst design for achieving high Pt utilization efficiency and high catalytic performance. [ABSTRACT FROM AUTHOR]