Continuous anodic oxidation was employed to alter the surface chemical properties of carbon fibers. As expected, the wetting behavior by water improved and that of non-polar liquid diiodomethane deteriorated. The calculated surface tensions mirror the changes in the physicochemical surface properties. The zeta (zeta)-potential measurements performed also reflect changes in the surface chemistry of the investigated carbon fibers. A correlation between the measured zeta-potentials and the wetting behavior of water on anodically oxidized carbon fibers was found. The influence of anodic carbon fiber oxidation on the epoxy composite properties was studied by a modified axial tensile test, which allows additionally the measurement of the so-called ＇notching force＇ as a measure of the interfacial composite properties. Common model-composite samples were used to check the reliability of this test. The determined ＇notching force＇ as a measure of adhesion correlates with the increased polar component of the fiber surface tension.