For investigating the influence of thermal treatment on the thermo-mechanical stability and the carbon fiber's surface composition, the T300 carbon fibers were thermally treated at temperatures ranging from 600 degrees C to 1500 degrees C. After treatment, the thermal stability and microstructure were analyzed by mass change and XRD measurement. The mechanical properties and the surface composition of carbon fibers were measured as a function of temperature by the single filament tensile test technique and ESCA analysis, respectively. The results indicated that T300 fiber had good thermal stability and high temperature mechanical properties. To some extent, the high temperature treatment could lead to a further graphitization of carbon fiber. The surface composition measured by ESCA revealed that the oxygen concentrations on the surface of fibers significantly decreased from 17.97% for as-received fiber to 1.97% for 1500 degrees C treated fibers. But the relative content of graphite-like carbon increased from 42.97% for as-received fibers to 53.13% for 1500 degrees C treated fibers. Such composition would result in a decreased surface activity of carbon fiber. (C) 2013 Elsevier B.V. All rights reserved.