Interfacial treatments of carbon fiber composites play a critical role in determining the overall performance as the surface of carbon fiber is smooth and inert causing low bonding to the polymer matrix. In this dissertation, atomic layer deposition (ALD) seeded ZnO nanowires were grown on carbon fiber as an enhanced interphase using two-step hydrothermal method for the first time. The effects of growth parameters of seed layers by ALD and nanowire growth in hydrothermal method were systematically investigated. Several morphologies of ZnO nanostructures were obtained and characterized using field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Single carbon fiber composites and carbon fiber composite laminates with ZnO nanowires were manufactured, then tested by single fiber fragmentation test, 3-point bending test, short beam 3-point bending test. It was found that the incorporation of ZnO nanowires significantly improved the mechanical properties of composites including interfacial shear strength, flexural strength and interlaminar shear strength by up to 286%,45.6% and 31.1%.The successful development and characterization of ZnO nanowires enhanced structural composites have great potential to lead to new generation of lightweight materials with increased mechanical properties for broad mechanical and aerospace engineering applications.