To provide a substrate for a light-emitting device, which is provided with a reflection layer having a high optical reflectance and being less susceptible to deterioration of the reflectance due to corrosion and which has an improved light extraction efficiency, and a light-emitting device employing such a substrate.A substrate for mounting a light-emitting element, which comprises a substrate main body having a mounting surface on which a light-emitting element is to be mounted, a reflection layer formed on a part of the mounting surface of the substrate main body and containing silver to reflect light emitted from the light-emitting element, and a vitreous insulating layer formed on the reflection layer, wherein the vitreous insulating layer contains a glass comprising, as its constituting components, at least SiO2, at least one of Al2O3 and B2O3, and an alkali metal oxide (containing at least one member selected from Li2O, Na2O and K2O), wherein by contents as represented by mol % based on oxides of the above components, (Li2O+Na2O+K2O)—Al2O3 is from −20 to 1.5%, and SiO2+3×Al2O3 is at most 90%.