When an adhesive joint is exposed to high environmental temperature. the load transmission capability of the adhesive joint decreases because the stiffness and strength of structural adhesive decrease. The load transmission capability of adhesive joint at high environmental temperature can be improved by increasing the surface free energy of adherends with surface pretreatments. In this paper, a capacitively coupled radio frequency plasma system was designed for the surface treatment of carbon/epoxy composites. The suitable plasma surface treatment conditions were experimentally investigated with respect to gas flow rate, vacuum pressure. power intensity. and surface treatment time through measurement of surface free energy by investigating strength of single lap composite adhesive joint. The surface free energy and adhesive joint strength were investigated with respect to the surface characteristics of the carbon/epoxy composite adherend measured with atomic force microscope. Also the failure mode of the composite adhesive joint was studied with respect to Surface treatment and environmental temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.