Existing research has shown that externally bonded fibre-reinforced polymer (FRP) reinforcement is an effective shear strengthening technique for reinforced concrete (RC) beams. One issue that has not been properly clarified by existing research is the size effect in RC beams shear-strengthened with FRP. Most of the existing experimental studies have been carried out on beams of small/medium size (e.g., with a beam height < 0.45m) and most of the existing shear strength models have been developed and substantiated using the test results of such small/medium-size beams. This paper presents the test results of 18 beams in 3 series corresponding to three different beam heights respectively: 300 mm, 600mm and 900 mm. Each series consisted of 6 beams, including a group of 3 beams with steel stirrups and another group of 3 beams without steel stirrups. Each group had 3 beams: an RC beam without strengthening (control specimen), a beam shear-strengthened with FRP U-strips, and a beam shear-strengthened with FRP full wraps. All the 18 beams had a shear span-to-depth ratio of 3.0. The test results showed that a significant size effect exists in RC beams shear-strengthened with FRP U-strips while the size effect is minimal when FRP full wraps are used. The test results also demonstrated that significant shear interactions exist among the different components (concrete, steel and FRP) of an FRP-strengthened RC beam.