In this research an evaluation method for the residual axial force of corroded high-strength bolts was investigated. Corroded high-strength bolts cut from a steel bridge were used for the measurement of thickness reduction and residual axial force. For the residual axial force measurement, a strain-gauge method with a core extraction was applied. An FE analysis examined the effect of the corroded shape of high-strength bolts on the residual axial force. The results reveal that the effect of corroded shapes on the residual axial force can be considered by using the thickness reduction amount near the washer for nut and bolt head. A proposed evaluation method based on the summation of thickness reduction can estimate the residual axial force of corroded high-strength bolts approximately.