A steady state current flowing in nematic liquid crystals (NLCs) has been studied for NLC cells with and without polyimide alignment layers. For the cell without the polyimide layers, the steady state current is ascribed to the charge injection from the electrodes and the generation of mobile ions at lower and higher applied voltages, respectively. For the cell with the polyimide layers, on the other hand, the current is much smaller than that of the cell without the polyimide layers. This is due to the fact that the polyimide layers block the charge injection from the electrode to the NLC slab and that the external applied voltage falls entirely in the polyimide layers.