The main object of this research is investigation on replacement of steel rebars with GFRP pultruded gratings in one-way concrete slabs. Since the deflection control is more important than the load control in civil engineering structures, this study focused on load-deflection behavior of concrete slabs. A closed-form relation for the load-deflection of a one-way slab is, at first, obtained by considering slab as an orthotropic plate with different stiffnesses in principal directions. In addition, the ultimate load capacity of slab reinforced with pultruded grating is calculated by modifying available theoretical equations for steel reinforcements. Using a finite element code, ANSYS software, with an exact nonlinear behavior of concrete and a 3-D failure criterion for cracking and crushing, the ultimate failure load and initial cracking load are estimated numerically. Also, a concrete slab reinforced with steel, the same extensional stiffness (E×A) as grating, is modeled to investigate the increasing of ultimate load. All the results are compared with the available data from other researches. The obtained results show that the replacing of steel reinforcement by FRP pultruded gratings is caused 12 percent increase in the ultimate load and 116.5 percent increase in the initial cracking load.