POLYANILINE (PANI) WAS SYNTHESIZED BY IN SITU OXIDATIVE PolymerIZATION METHOD USING AMMONIUM PEROXYDISULFATE (APS) AS OXIDANT AND HYDROCHLORIC ACID (HCL) AS DOPANT. THE PREPARED PANI HAS BEEN USED AS HOLE-INJECTION LAYER (HIL) IN Polymer light emitting diode (PLED). THE PLED WAS COMPOSED BY A THIN LAYERS OF POLY [2-METHOXY-5- (2’-ETHYL-HEXYLOXY)-1, 4-PHENYLENE VINYLENE] (MEH-PPV) AND PANI SANDWICHED BETWEEN INDIUM TIN OXIDE (ITO) AND ALUMINUM (AL) ELECTRODES, RESULTING IN THE DEVICE STRUCTURE ITO/PANI/MEH-PPV/AL. THE IMPROVED PERFORMANCE OF ITO/PANI/MEH-PPV/AL UPON THE FABRICATED DEVICES INCLUDING POLY (3, 4-ETHYLENEDIOXYTHIOPHENE): POLYSTYRENE SULFONATE (PEDOT:PSS) AS A HIL, ITO/PEDOT:PSS/MEH-PPV/AL, WAS INVESTIGATED. ACCORDING TO THE OBTAINED RESULTS, IT WAS SHOWN THAT THE PANI INJECTION LAYER YIELDS HIGHER CURRENT AND LOWER TURN-ON VOLTAGE. THE HOLE INJECTION BARRIER HEIGHT (J) OF THE FABRICATED PLEDS WAS ESTIMATED USING THE FOWLER-NORDHEIM (FN) FIELD-EMISSION TUNNELING THEORY.