Abstract: According to the ACI440.3R-04, the tests consisting of 90 glass fiber reinforced plastic (GFRP) rebars in 60 ℃ of the alkaline solution for 3.65, 18, 36.5, 92 and 183 d, were conducted to evaluate the tensile properties of GFRP rebars at different stress levels(0, 25%, 45%). The micro-formation of the GFRP rebars surface was surveyed by SEM. It indicates that the bonds between fibers and resin of GFRP rebars in the corrosion region becomes loose, and with the stress levels increase, the interfacial debonding between fiber and resin of GFRP rebars becomes more significant. After being exposed to alkaline solution for 183 d, tensile strength of GFRP rebars at stress level of 0 and 25% decreases by 48.81% and 55.56%, while tensile elastic modulus of GFRP rebars decreases by 5.47% and 5.73%, respectively, and GFRP rebars at 45% stress level have been already destroyed. The results of moisture absorption test show that the absorption kinetics is satisfactorily described by Fick's law. In addition, based on the Fick's law, the tensile strength prediction degradation model of GFRP rebars under alkaline solution was proposed.