There is provided a ceramics substrate for mounting a light-emitting element having high thermal conductivity which can achieve high reflectance and which can enhance heat dissipation performance to extend the lifetime of a light-emitting element. A ceramics substrate for mounting a light-emitting element includes a ceramic sintered body, the ceramic sintered body having a mounting section on which a light-emitting element is mounted, in a surface portion on a mounting section side of the ceramic sintered body, a ratio of crystal grains having a crystal grain size of 0.2 µm to 1.0 µm in equivalent circle diameter being in a range of 45% to 80%, a ratio of crystal gains having a crystal grain size of 2.0 µm to 6.0 µm in equivalent circle diameter being in a range of 5% to 15%, and a ratio of crystal grains having a crystal grain size of more than 6.0 µm in equivalent circle diameter being 2.7% or less. Therefore, the reflectance of the ceramics substrate for mounting a light-emitting element (1) can be improved, and a ceramics substrate for mounting a light-emitting element with high thermal conductivity can be produced.