As the applications of composite structures have increased, various techniques to join composite parts to the structures have been developed in order to meet the required adhesion strength. In this work, surface modification of carbon/epoxy composites was investigated using ultraviolet (UV) surface treatment to increase the adhesion strength between the carbon/epoxy composite and the epoxy adhesive. After UV surface treatment, X-ray photoelectron spectroscopy (XPS) analysis and contact angle measurements were performed to analyze the surface characteristics of the carbon/epoxy composites. From the results of XPS analyses and adhesion strength tests, it was found that the increase of C=O bond density on the surface of carbon/epoxy composite caused the enhancement of adhesion strength. Also it was found that the UV-B (wavelength 280-315 nm) surface treatment resulted in a superior adhesion strength compared to the UV-A (wavelength 315-400 nm) surface treatment.