Steel tire cords were coated via RF plasma polymerization of acetylene and butadiene gas in order to enhance adhesion to rubber compounds. Adhesion of tire cords was measured by TCAT and T-test as a function of type of gas, plasma powder, treatment time, gas pressure and Ar gas etching. Some samples were subjected to aging study in distilled water at 80℃ for a period of 7 days. After testing, tire cords were analysed by SEM to elucidate the adhesion mechanism. The highest adhesion values were obtained at 20W, 2min and 25mtorr for acetylene plasma polymerization, and 10W, 4min, 25mtorr for butadiene plasma polymerization. However, Ar plasma etching did not affect adhesion, while the adhesion of tire cords increased rather than decreased, contrary to expectations. It was not possible to elucidate failure mode by SEM, owing to the rough surface of the tire and the thin plasma polymer coating layer.