Temperature-dependent current-voltage characteristics of organic light-emitting diodes(OLEDs) were studied in a device structure of ITO/TPD/Alq$_3$/Al to understand conduction mechanism. The current-voltage characteristics were measured in the temperature range of 8K ~ 300K. We analyzed an electrical conduction mechanism of the OLEDS using space-charge-limited current(SCLC) and Fowler-Nordheim tunneling. In the temperature range above 150k, the conduction mechanism could be explained by space charge limited current from the inversely proportional temperature dependence of exponent m. The characteristic trap energy is found to be about 0.15ev. At low temperatures below 150k, the Fowler-Nordheim tunneling conduction mechanism is dominant. We have obtained a zero field barrier height to be about 0.6~0.8eV.