A nitride semiconductor light emitting device includes n-type and p-type nitride semiconductor layers, and an active layer disposed between the n-type and p-type nitride semiconductor layers and having a stack structure in which a plurality of quantum barrier layers and one or more quantum well layers are alternately stacked. A net polarization of the quantum barrier layer is smaller than or equal to a net polarization of the quantum well layer. A nitride semiconductor light emitting device can be provided, which can realize high efficiency even at high currents by minimizing the net polarization mismatch between the quantum barrier layer and the quantum well layer. Also, a high-efficiency nitride semiconductor light emitting device can be achieved by reducing the degree of energy-level bending of the quantum well layer.