The continuous anodic oxidation of high modulus (HM) carbon fibres in sulphuric acid electrolyte, with varied concentrations as a possible surface treatment method, is presented. It can be shown that within the applied potential ranges and the resulting current densities no loss of mechanical fibre properties or increase in BET surfaces is observable. The formed surface oxides are detected by a thermal fibre decomposition treatment up to 1000° C and thus give an explanation for the increase in ILSS (interlaminar shear strength) caused by the different applied current densities. It is also shown that the specific electric charge (current density x pretreatment time) of a particular electrolyte concentration can be taken as a parameter to describe the surface activation by anodic oxidation and its consequent influence on the ILSS of composites fabricated from treated carbon fibres in epoxy polymer. However, this fibre activation is predominantly affected by the concentration of the electrolyte.