The effectiveness of structural macro-synthetic polyolefin (PO) and a hybrid combination of steel and synthetic fibers on the flexural performance of glass fiber-reinforced polymer (GFRP) reinforced concrete beams is studied. Improvement in post-cracking stiffness, deformation factor, and change in failure modes due to fiber addition is investigated. In total, 14 full-scale RC beams are cast and tested under four-point bending configuration. The test series includes: 1) control specimen with GFRP reinforcement; 2) GFRP-reinforced members with 0.35, 0.70, and 1.0% volume of PO fibers; and 3) GFRP-reinforced members with 0.35, 0.70, and 1.0% volume of hybrid steel and PO fibers in equal ratio. Experimental results revealed that the addition of synthetic and hybrid fibers significantly improved the post-cracking stiffness, peak strength, and energy dissipation capacity of GFRP-reinforced members. The deflection levels at service loads reduced with increase in fiber dosage. Deflection of GFRP-reinforced members with and without fibers was calculated using the models proposed by different researchers and compared with test results at the serviceability levels. Also, a proposed model is introduced for consideration of the effect of fiber contribution in the predictions of deflection. © 2020 American Concrete Institute. All rights reserved.