One‐pot synthesis of carbon‐supported Pd‐Au alloy nanoparticles with well‐defined dendritic shape (Pd‐Au_den/C) was achieved by co‐reduction of K₂PdCl₄/HAuCl₄ mixtures in a molar ratio of 1:1 with hydrazine in the presence of Vulcan XC‐72R. The prepared Pd‐Au_den/C exhibited significantly enhanced performance in the electrocatalytic oxidation of ethanol compared with dendritic Pd nanoparticles and a commercial Pd/C catalyst. Pd‐Au_den/C even showed higher durability in electro‐oxidation of ethanol than the supported catalyst prepared by the deposition of presynthesized dendritic Pd‐Au nanoparticles on the carbon support. The experimental results clearly indicate that enhanced interaction between nanoparticle catalysts and carbon support through the one‐pot synthesis protocol can improve the durability of the electrocatalysts.