Among the unresolved issues in the design of structural concrete reinforced with fiber reinforced composite (FRP) bars, the understanding of size effect in the reduction of the shear strength of deep beams without shear reinforcement is of fundamental and practical significance. Size effect accrues primarily from the larger width of diagonal cracks as the effective depth is increased, and has been extensively documented in the case of steel reinforced concrete (RC) through a number of laboratory tests. In FRP RC, the lower longitudinal elastic modulus of the flexural reinforcement results in deeper and wider cracks. Yet, the calibration of any of the current semi-empirical design algorithms is based on test results of beams and one-way slabs with maximum effective depth of 360 mm, which is not representative of relevant large-scale applications. This paper presents and discusses the results of laboratory testing of large-size and scaled FRP RC beams without shear reinforcement, having maximum effective depth of 147, 294 and 883 mm, and effective reinforcement ratio of 0.12% and 0.24%. It is shown that the shear strength of the large-size specimens with less flexural reinforcement decreases on average by 55% compared with the smaller specimens. However, the conservativeness of the current design algorithms generally offsets the size effect. The provisions of the UK Institution of Structural Engineers (ISE) and the Italian National Research Council (CNR) provide the most accurate estimates, where the former yields more conservative and consistent results.