The effect of a relatively high concentration of KOH solution (4M) on the mechanical properties and chemical stability of carbon fiber-reinforced epoxy resin composites, prepared with different volume fractions of reinforcement, were investigated. Upon treatment of specimens of such composites with the KOH solution at different temperature and for different durations, their tensile strengths were adversely affected to varying degrees, depending on treatment conditions and volume percent of carbon fiber reinforcement used. Surfaces of treated specimens were examined for matrix stability, fiber disruption, and debonding. Optical microscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate chemical and mechanical degradation of these composites. Results clearly showed that prolonged exposure of composite specimens to such aggressive environments markedly increased the degradation of their mechanical properties. On the other hand, these results also showed that increasing the volume fraction of the carbon fiber reinforcement reduced the severity of degradation of these composite and enhanced their mechanical stability. (c) 2005 Wiley Periodicals, Inc.