This study investigates the influence of beam size on the contribution of fiber reinforced polymers (FRP) used for shear-strengthening of deficient reinforced concrete (RC) beams. The experimental program considers twelve RC T-beams divided in two groups with two different sizes (200 and 400 mm) shear-strengthened with carbon FRP sheets. The ratio of beam dimensions between the two groups is 1:2. Two beams of each group are used as benchmarks and their behavior is compared with the beams strengthened with a U-wrap configuration. In order to investigate the influence of the presence of steel stirrups on the size effect, each beam size includes beams with steel stirrups and others without steel stirrups. The test results clearly show that the shear resistance of the beams with no steel stirrups, strengthened in shear with FRP, is influenced by the beam size. The beams with steel stirrups are less influenced by the beam size since the shear capacity is strongly dominated by the steel stirrups contribution.