A Group III nitride semiconductor light-emitting device includes a sapphire substrate; and an n contact layer, an n cladding layer, a light-emitting layer, a p cladding layer, and a p contact layer, each of the layers being formed of Group III nitride semiconductor, are sequentially deposited on the sapphire substrate. The n cladding layer includes two layers of a high impurity concentration layer and a low impurity concentration layer in this order on the n contact layer, and the low impurity concentration layer is in contact with the light-emitting layer. The low impurity concentration layer is a layer having a lower n-type impurity concentration than that of the high impurity concentration layer, which has an n-type impurity concentration of 1/1000 to 1/100 of the p-type impurity concentration of the p cladding layer and a thickness of 10 Å to 400 Å.