The method of high temperature and pressure ammonia solution treatment to improve the interfacial performances of carbon fiber/epoxy composites is discussed in this study. Besides, the influence of high temperature and pressure ammonia solution treatment on carbon fiber and its reinforced epoxy composite interface performance were studied. The untreated and treated carbon fibers were characterized by monofilament tensile test, X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). The interfacial adhesion of the untreated and treated carbon fibers reinforced epoxy resin composites were also evaluated by interface shear strength (IFSS) test, interlaminar shear strength (ILSS) test, and fracture morphology analysis. It was found that the interfacial adhesion of composites increased greatly after high temperature and pressure ammonia solution treatment. The improvement of interfacial adhesion was attributed to the increase of polar functional groups and surface roughness of carbon fibers surface after treatment. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3436-3441, 2009