In this work the effect of atmospheric plasma treatment on carbon fiber has been studied. The carbon fibers were treated for 1, 3 and 5 min with a He/O(2) dielectric barrier discharge atmospheric pressure plasma. The fiber surface morphology, surface chemical composition and interfacial shear strength between the carbon fiber and epoxy resin were investigated using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) and the single fiber composite fragmentation test. Compared to untreated carbon fibers, the plasma treated fiber surfaces exhibited surface morphological and surface composition changes. The fiber surfaces were found to be roughened, the oxygen content on the fiber surfaces increased, and the interfacial shear strength (IFSS) improved after the atmospheric pressure plasma treatment. The fiber strength showed no significant changes after the plasma treatment. (C) Koninklijke Brill NV, Leiden, 2011