Using discrete steel fibers in reinforced concrete improves some mechanical properties of concrete such as the tensile strength, shear strength, toughness and the flexural strength. In this research work, the effect of adding steel fibers on the moment capacity of steel fiber reinforced concrete (SFRC) is studied and new relationships accounting for the variations in the modulus of rupture resulted from the added steel fibers are presented. The relations are expressed in terms of the fiber content, fiber aspect ratio and the concrete compressive strength and then employed in predicting the moment capacity of SFRC beams. The applicability of the proposed formula in predicting the moment capacity of SFRC beams is checked by analyzing fifty-two beams of different fiber content, concrete strengths and densities ranging from normal to light-weight. The comparisons of the predictions agreed with the corresponding experimental values.