In the present work four different methods of investigation were used to characterize the surfaces of treated glass fibres. The capillary rise technique and the inverse gas chromatography (IGC) are methods to determine the surface free energy of solids. The zeta potential measurement gives information about the chemical properties of solid surfaces. In addition, the coating homogenity was investigated by field-emission scanning electron microscopy (FE-SEM). Glass fibres with four different treatments were used in this work: polyethylene-(PE)-dispersion treated fibres, polyurethane/aminosilane-dispersion treated fibres, fibres treated with an epoxy resin/aminosilane-dispersion and fibres with a cationic silane treatment. FE-SEM has shown that the surfaces of the glass fibres were completely covered by the polyethylene and the cationic silane. The polyurethane and the epoxy-resin covered only a part of the glass fibre surface. A statement about the distribution of the aminosilane cannot be made, because the thickness of the monolayer is less than the resolution of the FE-SEM. Zeta potential, IGC and capillary rise technique measurements lead to comparable results about the different chemical properties of the glass fibres.