Carbon (C) fibers have important advantages because of their high strength, high stiffness, specific fatigue behavior and lower density. The fiber and the epoxy interaction is always a problem for many composite systems including other fibers. The fiber/matrix interaction can be improved by using physical and chemical treatments in order to achieve enhanced interfacial and interlaminar properties. Interlaminar properties are key factors for the high performance of carbon fiber composites. The surface treatment of carbon fibers to create active surfaces for the sizing agent and improved composite performance is one of the most important aspects of carbon-fiber-reinforced composites. In this study, the effects of carbon fiber surface treatment with ammonium carbonate ((NH4)(2)CO3) at various concentrations and silane sizing on the carbon fiber surface were investigated. The surface characteristics of carbon fiber were examined using X-ray photoelectron spectroscopy (XPS). The effects of these surface modifications on the tensile strength, flexural strength, interlaminar shear strength and morphological properties of carbon-fiberreinforced composites were also studied. XPS indicated that the surface-treated carbon fibers had higher oxygen (O) concentration and higher oxygen/carbon ratio than the untreated carbon fibers. All surface treatments were shown to improve the tensile, flexural and interlaminar shear strengths of the composites.