In preparing switchable mirrors, palladium (Pd) was used as a catalyst for hydrogenation and dehydrogenation, and to prevent oxidation of the switchable layer. To reduce the cost, Pd was alloyed with ruthenium (Ru) and used as a catalytic layer, since the price of Ru is approximately one-tenth that of Pd. Switchable mirrors of magnesium-yttrium(Mg-Y) alloy thin films coated with a Pd-Ru layer were prepared by direct-current magnetron sputtering method. Their optical switching properties between reflective and transparent states were studied using gasochromic method. The mirrors coated with Pd1-alpha Ru alpha of up to alpha approximate to 0.6 showed nearly the same switching time from reflective to transparent state as those coated with pure Pd, while the mirrors coated with Pd1-alpha Ru alpha of 0.2 5 <= alpha 5 <= 0.4 showed shorter switching times from transparent to reflective state than those coated with pure Pd. Furthermore, the alloy-coated mirrors with shorter switching times had approximately 2-3 times higher switching durability than those coated with pure Pd. These shorter time and higher durability may be because Pd-Ru alloy prevents oxidation of the underlying layers more effectively than pure Pd. Thus, Pd-Ru alloy is one of the most promising catalysts for switchable mirrors.