A GaN-based semiconductor light-emitting element is provided and includes a first GaN-based compound semiconductor layer; an active layer having a multi-quantum well structure; and a second GaN-based compound semiconductor layer. At least one of barrier layers constituting the active layer is composed of a varying-composition barrier layer, and the composition of the varying-composition barrier layer varies in the thickness direction thereof so that the band-gap energy in a region of the varying-composition barrier layer, the region being adjacent to a boundary between a well layer disposed closer to the second GaN-based compound semiconductor layer and the varying-composition barrier layer, is lower than that in a region of the varying-composition barrier layer, the region being adjacent to a boundary between a well layer disposed closer to the first GaN-based compound semiconductor layer and the varying-composition barrier layer.