One of the major disadvantages of ultra-high modulus polyethylene (UHMPE) fibers is their low surface energy which makes them difficult to adhere to most of the resins used in composites. Therefore, UHMPE fibers are often treated with plasmas to improve their surface properties. However, aging of plasms treatment effect is a major concern for plasma-treated fibers. In this study, UHMPE fibers were treated for 30, 60, 90, and 120 s with Ar/O-2 plams on a dielectric barrier discharge device. The change of the surface properties and adhesion characteristics of the fibers were investigated immediately after and 30 days after the plasms treatments using X-ray photoelectron spectroscopy, contact angle measurement, scanning electron microscopy, and micro-bond tests. Results show that aging of the plasma treatment effect was suppressed by increasing the plasma treatment duration. The interfacial shear strengths were increased from 4 MPa to 5.9, 7.8, 9.2, and 7.6 MPa for the 30, 60, 90, and 120 s treatment groups lowered 24, 22, 10, and 9%, respectively. Increasing the plasma treatment time will increase the thickness and saturation degree of the oxidized layere on the polymer surfaces, which might hinder the migration of the hydrophobic polar functional groups from the surface to the bulk of the polymer after the plasma treatment. (c) 2008 Wiley Periodicals, Inc.