A nitride semi-conductor light emitting device has a p-type nitride semi-conductor layer 7, an n-type nitride semi-conductor layer 3, and a light emission layer 6 which is interposed between the p-type nitride semi-conductor layer 7 and the n-type nitride semi-conductor layer 3. The light emission layer 6 has a quantum well structure with a barrier layer 6b and a well layer 6a. The barrier layer 6b is formed of AlaGabIn(1-a-b)N (0 0), and contains a first impurity at a concentration of A greater than zero. The well layer 6a is formed of AlcGadIn(1-c-d)N (0 0), and contains a second impurity at a concentration of B equal to or greater than zero. In the nitride semi-conductor light emitting device of the present invention, the concentration of A is larger than that of B, in order that the barrier layer 6b has a concentration of oxygen smaller than that in the well layer 6a.