In this study, aramid, Heracron (R), which was purchased from Kolon Inc., Korea, and phenol composites were prepared by plasma treatment and the influence of this plasma treatment on their mechanical properties and ballistic behavior were ascertained. By measurement of water contact angle and XPS analysis, we find that the plasma treatment may help the incorporation of functional oxygen groups on the surface of the Heracron (R) fabrics. Additionally, the surface roughness of Heracron (R) fiber may be proportional to the plasma treatment times. By SEM and mechanical tests, it was shown that plasma-treated Heracron (R)/phenol composites exhibited higher mechanical properties compared with plasma-untreated Heracron (R)/phenol composites. Based on this finding, we can conclude that plasma-treatment can promote the interfacial adhesion between Heracron (R) and phenol, resulting in the superior mechanical properties of their composites. However, the ballistic behavior conflicted with the mechanical properties. That is to say, a helmet, manufactured from the plasma-treated Heracron (R)/phenol composites, exhibited lower ballistic properties than that of the plasma-untreated Heracron (R)/phenol composites. As a result, we demonstrated that for ballistic application, somewhat weak fiber-matrix adhesion leads to the improved ballistic behavior. However, it becomes apparent that the optimum strength condition for the composite interphase depends on the particular application, thus increased fiber-matrix adhesion may be more appropriate. (c) Koninklijke Brill NV, Leiden, 2011