Bimetallic Au@Pt nanoparticles (NPs) with Pt monolayer shell are of much interest for applications in heterogeneous catalysts because of enhanced catalytic activity and very low Pt-utilization. However, precisely controlled synthesis with uniform Pt-monolayers and stability on the AuNPs seeds remain elusive. Herein, we report the controlled deposition of Pt-monolayer onto uniform AuNPs seeds to obtain Au@Pt core–shell NPs and their Pt-coverage dependent electrocatalytic activity for methanol electro-oxidation. The atomic ratio between Au/Pt was effectively tuned by varying the precursor solution ratio in the reaction solution. The morphology and atomic structure of the Au@Pt NPs were analyzed by high-resolution scanning transmission electron microcopy (HR-STEM) and X-ray diffraction (XRD) techniques. The results demonstrated that the Au@Pt core–shell NPs with Pt-shell thickness (atomic ratio 1:2) exhibit higher electrocatalytic activity for methanol electro-oxidation reaction, whereas higher and lower Pt ratios showed less overall catalytic performance. Such higher catalytic performance of Au@Pt NPs (1:2) can be attributed to the weakened CO binding on the Pt/monolayers surface. Our present synthesis strategy and optimization of the catalytic activity of Au@Pt core–shell NPs catalysts provide promising approach to rationally design highly active catalysts with less Pt-usage for high performance electrocatalysts for applications in fuel cells.