In composites carbon fibers are used as reinforcing fibers with thermosetting and thermoplastic resins as matrices. These carbon fibers differ greatly in their microstructure and thus in their properties. To achieve adequate composite properties, special carbon fiber surface treatment methods are necessary. This paper describes a systematic study on oxidative surface treatment of carbon fibers by wet, dry and anodic oxidation. Further investigations by matrix variation reveal the influence of the matrix strength on the mechanical properties of the composites. Finally, it is shown that in the case of impact load composite fracture behavior is controlled only by the fiber itself.