There are provided a light-emitting element mounting substrate having high bonding strength between a substrate main body and a metal portion, and a light-emitting device having high bonding strength between the substrate main body and the metal portion and high reliability. A light-emitting element mounting substrate includes a substrate main body (20) formed of a ceramic sintered body; and a silver-containing metal portion (2), a silver-containing region (4) existing in a portion of the substrate main body which faces the metal portion across a bonding portion bonding the substrate main body and the silver-containing metal portion. Accordingly, it is possible to increase bonding strength between the substrate main body (20) and the metal portion (2).