Strong metal-support interaction (SMSI) over Ru/CaAlOx was constructed by utilizing the surface structural reconstruction of Ca-Al layered double hydroxides (LDHs) in aqueous solution and their subsequent hydroxide-to-oxide transformations. Ru nanoparticles were found to uniformly embed with CaAlOx. The electronic interactions and changes in CO adsorption behavior confirmed the SMSI state between Ru and CaAlOx. Owing to SMSI, the as-prepared Ru/CaAlOx showed improved catalytic activity in the decomposition of ammonia, especially at a relatively low temperature.