The effect of surface treatment at high temperatures on the morphology and mechanical behavior of Torayca T300 carbon fiber is studied. It is found that the surface treatment results in a considerable change in the surface and cross-sectional morphology of the carbon fiber. Accordingly, there are sizable change in mechanical properties of the fiber: in particular, compressional failure mechanism changes from buckling to simple shear mode as the surface treatment temperature increases. There is not an apparent relationship between the surface structural parameters such as surface area, pore volume, etc. and the mechanical properties such as tensile and compressive strengths.