This study aimed to investigate the effectiveness of CFRP sheet in inhibiting the corrosion process of steel reinforcement embedded in RC columns. a total of 30 small-scale RC columns were conditioned under the accelerated corrosion process and then tested under uni-axial compression up to failure. Some of the columns were strengthened with CFRP sheets prior to the beginning of the accelerated corrosion process to simulate newly constructed RC columns wrapped with CFRP sheets. the others were strengthened with CFRP sheets after a certain period of the accelerated corrosion process to duplicate the corrosion-damaged RC columns to be repaired by wrapping with CFRP sheets. During the accelerated corrosion process, corrosion rate was monitored. the test results showed that although CFRP sheet wrapping decreased the corrosion rate, the corrosion of steel reinforcement could continue to occur. Based on the small-scale RC column tests, design guidelines were proposed and the proposed design guidelines were validated through test results of 4 mid-scale RC columns. the proposed design guidelines introduced a concept of equivalent area to account for the corrosion-damage such as internal cracking and cross-sectional loss of steel reinforcement.