Chemical modifications of the surface of Kevlar fiber were investigated as a means of improving fiber-matrix adhesion. The fiber surface was used as a polymerization support for interfacial polycondensation. Nylon-6,6 was successfully polymerized in this way. The grafted nylon was characterized by ESCA (electron spectroscopy for chemical analysis), DSC (differential scanning calorimetry), and extraction procedures. An increase of the transcrystalline layer thickness was observed through optical microscopy, indicating better fiber-matrix adhesion. Both plasma treated fibers having been submitted or not to chemical treatments were used as reinforcements for nylon-6,6 unidirectional composites. Improvement of the mechanical properties were related to better interfacial interactions due to grafted nylon chains.