The electron and hole drift-mobilities of tris(8-hydroxy-quinolinato) aluminium (Alq(3)) thin films have been determined using impedance spectroscopy (IS) measurements. The theoretical basis of drift-mobility measurement with IS rests on a theory for single-injection space-charge limited current. The electron drift-mobilities in Alq(3) which measured from the frequency dependence of both capacitance and conductance had the same electricfield dependence and were identical to those measured by a time-of-flight (TOF) transient photocurrent technique. To estimate the hole drift-mobility in Alq(3), a 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl thin film was inserted as an injection layer to reduce the hole injection barrier between an injection electrode and the Alq(3) thin film. The hole drift-mobilities of Alq(3) thin films measured with IS were identical to those measured by the TOF method. These results are essential for clarifying the mechanism of the carrier transport of organic light emitting diodes (OLEDs) with the aim of improving OLED performance. (C) 2013 Elsevier B.V. All rights reserved.