Supported alloy catalysts have been extensively applied to many significant industrial chemical processes due to the abundant active sites with distinguishable geometry and electron states. However, a detailed in situ investigation of the interaction between support and alloy nanoparticles is still lacking. Here, a subversive ‘tearing effect’ on the interface of TiO ₂ ‐supported NiRu alloy nanoparticles is in situ discovered by environmental transmission electron microscopy (ETEM) with a dramatic redispersion process of alloy nanoparticles from ~25 nm to 2–3 nm under the repeated hydrogen reduction. Dual‐driven by the distinct alloy‐support interaction involving the restructuring of alloy nanoparticles and growth of TiO _x overlayer, larger NiRu alloy nanoparticles spontaneously disintegrate into atoms migrating on support. Atoms are finally captured by the defects generated on TiO ₂ during the repeat reduction, which also confines the further growth of the newly alloy nanoparticles. Owing to this specific alloy‐support interaction, smaller alloy nanoparticles on TiO ₂ support are much more stable than the bigger ones, which holds promise for industrial applications as durable catalysts. This novel metal‐support interaction with the ‘tearing effect’ revealed on supported alloy catalysts provides new knowledge on the structure‐performance relationships in all the alloy catalysts for hydrogenation reactions.