Knowledge of the behavior of precast concrete box culverts (PCBC) reinforced with glass fiber-reinforced polymer (GFRP) bars is still in its early stages and has been studied in a few articles. The current study examined the behavior of PCBC with GFRP reinforcement under shear. Two full-scale PCBC specimens were constructed and tested under CL-625 truck wheel load at critical shear location, as stipulated by the Canadian Highway Bridge Design Code (CHBDC) (CAN/CSA S6-19 in Canadian highway bridge design code. Canadian Standards Association, Mississauga, Ontario, Canada [1]) One specimen was reinforced with GFRP-reinforcing bars, while the other was reinforced with steel-reinforcing bars, both with the same reinforcement ratio of 0.83%. Both specimens had a span and rise of 1500 mm, and a joint length of 1219 mm. The slabs and walls were 150 mm thick, and the dimensions of the haunches were equal to the wall thickness. The findings show that using GFRP bars as internal reinforcement for PCBCs provides high load-carrying capacity that exceeds the ultimate design factored live load. This study suggests that GFRP bars can be a better alternative to steel reinforcement in PCBC applications.