The main objective of the research is to study the preparation of one way slabs of ordinary concrete, and then to prepare concrete slabs by replacing the main reinforcing steel with two kinds of steel fibers (ordinary steel fibers and recycled steel fibers) by fraction volumes of 0.125, 0.250, and 0.375%. Also, study the mechanical properties of the mixtures as a ompressive strength, indirect tensile strength, and flexural strength. Concrete slabs of these mixtures have been prepared with specific geometrical dimensions700 * 300 * 70 mm, exposed to line load, to study the bending moment and maximum failure load of these slabs. A concrete mixture was produced after proportionment based on the ACI and casting six cubes tested at the ages of 7 and 28 days where the strength requirements for design were achieved. The main mixtures of research were produced, three cubes for compressive strength testing, twenty one cylinders for indirect tensile strength testing, and twenty one prisms for modulus of rupture testing. Also sixteen concrete slabs were prepared, two of them were reference slabs without reinforcing steel, the other two with main reinforcing steel only, six of them replaced by the main reinforcing steel with ordinary steel fibers, and the last six replacing the main reinforcing steel with recycled steel fibers. The results showed that both the failure load and the resultant deflection in concrete slabs decreased by (20.09%, 51.91%) for maximum load and by (35.18%, 81.48%) compared to the reference slabs when replacing the main reinforcing steel with steel fiber, also by (25.72%, 38.29%) to failure load and (38.88%, 79.63%) for the deflection compared to the reference slabs when replacing the main reinforcing steel with recycled steel fibers. The best value for maximum load and deflection could be obtained from this study was at 0.125% replacement ratio of the main reinforcing steel with recycled steel fibers, the highest value of ductility was 3.77 at the replacement ratio of 0.250% of the main reinforcing steel with the ordinary steel fibers, also the highest hardness value was 11.67 kN / mm with the replacement ratio of 0.125% of the main reinforcing steel with recycled steel fibers and increased by 61.85% than the hardness of the reference slabs.