To provide a substrate for mounting a light-emitting device, which is provided with a silver reflection layer having a high reflectance and being less susceptible to deterioration of the reflectance due to corrosion and which has an improved light extraction efficiency.A substrate for mounting a light-emitting element 1, which comprises a substrate main body 2, a silver reflection layer 6 composed mainly of silver or a silver alloy, formed on the substrate main body 2, and a protective layer formed so as to cover the entire surface of the silver reflection layer 6, wherein the protective layer 7 contains an alumina filler and further contains a glass constituting the protective layer 7, having silver ions diffused therein. The concentration of silver ions contained in the glass of the protective layer 7 is at least 0.5 mass % and at most 5.0 mass %.