We have investigated dielectric properties depending on bias voltage in organic light-emitting diodes using 8-hydroxyquinoline aluminum $(Alq_3)$ as an electron transport and emissive material. We analyzed the dielectric properties of organic light-emitting diodes using impedance of characteristics. Impedance characteristics was measured complex impedance Z and phase $ heta$ in the frequency range of 40 Hz to $10^8$ Hz. We obtained complex electrical conductivity, dielectric constant, and loss tangent $(tandelta)$ of the device at room temperature. From these analyses, we are able to interpret a conduction mechanism and dielectric properties contributed by an interfacial and orientational polarization.