We have used ITO/Alq3/Al structure to study electrical conduction mechanism in Alq3 based organic light emitting diode. Current-voltage characteristics were measured at room temperature by varying the thickness of Alq3 layer from 60 to 400nm. We were able to prove that there are three different mechanism depending on the applied voltage; Ohmic, SCLC (space-charge-limited current). and TCLC (trap-charge -limited current) mechanism.