Abstract: PBO super fibre is submitted to a corona treatment, and the properties of the interphase between PBO fibres and epoxy matrix systems are optimized by a surface treatment process of the fibres. The relation is studied between this surface treatment and the resulting chemical and physical surface structure, as measured with XPS,FT-IR,SEM and surface wettability. The adhesion strength in fibre-epoxy systems, as measured with single-fibre pull-out and short beam shear experiments, has been established and related to the macromechanical data of real composites. It is concluded that corona-treated fibres may cause 25.6% improvement in the interfacial shear strength(IFSS) due to the increase of the oxygen surface content and the well wettability to water. But the short beam shear strength values from the corona-treated and untreated fibres showed only small differences.