This paper pointed to examine the glass fiber reinforced polymer bars effect on behaviour of flexural of lightweight aggregate concrete. Tests of flexure behaviour on beams were under four points in bending with total number of samples eight beams. The impact of type of reinforcement “glass fiber reinforced polymer reinforcement" that used in top and bottom reinforcing of beams, concrete strength, and concrete type were studied. The parameters that used in this study are maximum load, failure mode, flexural capacity, deflection, and stiffness of the tested beams were investigated. Using glass fiber reinforced polymer bars has more advantages like high longitudinal tensile strength, non-toxic, non-conductivity, lightweight, and doesn't have any corrosion. Using lightweight aggregate concrete by replacement coarse aggregate with pumice because this aggregate has low density, so the concrete weight decreased for the same strength and that lead to decreasing own weight so decreasing concrete sections and total cost of building. Experimental results showed that any concrete beams reinforced with glass fiber have greater deflection and strain than reinforced with steel and at any reinforcement type normal beams have deflection and strain mor than lightweight aggregate concrete.