The purpose of this study is to evaluate the flexural behavior of Reinforced Concrete (RC) beams strengthened with prestressed Carbon Fiber Reinforced Polymers (CFRP) plates and to suggest the analytic equations of flexural capacity calculation for strengthening design. The evaluation of flexural behavior is carried out by parameter study experiments and the derived design equations are verified by the experimental results. The experimental parameters are concrete compressive strength, tensile reinforcement ratio, and prestressing level. Failure and fracture modes are observed and the efficiency of different CFRP prestressing level is studied. The results show that the non-prestressed specimens fail by spalling of the CFRP plate from the RC beam, while prestressed specimens fail due to CFRP plate failure. The presented equations of flexural capacity for RC beams strengthened with prestressed CFRP plates are shown to be sufficiently accurate in predicting flexural strengthening effectiveness of RC beams.