For applications in the civil and building engineering area of the retrofitting method using carbon-fiber sheet, the behavior of durability and long-term performance of reinforced concrete members under live loads should be grasped. This paper describes about the long-term performance of reinforced concrete beams with carbon-fiber sheet. As a result of long-term lending tests for the last 4 years, it was concluded that the retrofitting system using carbon-fiber sheets is successful to increase the flexural strength and to prevent the increase of long-term deflection on the existing reinforced concrete beams or slabs, in the manner as seismic reform of columns in buildings and the pier of bridges.