An investigation has been carried out concerning the influence of water absorption on the mechanical properties and fatigue properties of carbon fiber/polyamide (CF/PA) composites.Tensile and tension-tension fatigue tests were conducted on both dry and wet specimens, which had been preconditioned in laboratory and in water for 10 days, respectively.Mechanical properties were decreased 20% in tensile strength and 10% in youngs modulus by water absorption.Fatigue strength was decreased by water absorption.