A water-soluble conducting polymer (CPP400 PASTE) containing a derivative of polythiophene with several dopants has been investigated as an anode material for organic electroluminescent (EL) devices. Electroluminescent (EL) and current-bias voltage (I-V) characteristics of devices with a structure of ITO/CPP400 PASTE/TPD/Alq(3)/Li:Al were measured. It was found that the rum-on voltage, current density, and luminance of the devices were dependent upon the thickness of CPP400 PASTE film. This phenomenon was explained by the energy level diagram of the device.