Polyethylene terephthalate fibers cords were modified with argon, oxygen, and successive argon/oxygen cold plasmas as a function of treatment time. Plasma treated cords were coated with resorcinol formaldehyde latex, then tested as rubber reinforcing materials. The peel strength was discussed with respect to the polar component of the surface energy and the etching of the fibers. An increased adhesion of similar to 280% was obtained with 30 min argon plasma followed by 30 min oxygen plasma, at 75 W power and 40 Pa pressure without altering the traction strength of the fibers cords.